By examining the heart of a crocodile, researchers have discovered how it is that an air-breathing land animal can manage to glide through murky waters for several hours without the need to surface.

There is that one scene in documentaries that we often come across on television: Crocodiles gliding gracefully inside the water, waiting for hours for the perfect time to pounce and snatch their prey from their necks and into the water. But how do these animals manage to stay underwater for almost two hours without surfacing for air even though they, just like human beings and other land animals, live on pulmonary respiration and are in need of the free oxygen in the air?

A member of the reptiles class, crocodiles do not have gill nor can they have skin respiration since their skin is covered with a thick and airtight keratin armor. Just as every living organism are provided with a suitable anatomic and physiological character for their survival, crocodiles are also granted with a system that facilitates their long stay in the water.

Crocodiles are bestowed with a special heart anatomy different to other reptiles like lizards, tortoises, and snakes. The hearts of other reptiles are designed to contain three sections including two atriums and one ventricle. The right atrium, which collects the returned oxygen-deprived (deoxygenated) blood and the left atrium which collects the oxygen-rich (oxygenated) blood retrieved from pulmonary arteries of the lung, transports the blood to one common ventricle. Because there is only one ventricle to receive and combine oxygenated and deoxygenated blood, a mixture of less oxygenated blood is pumped to their body. Depending on outside temperature, the body temperature of a reptile increases or decreases. Their metabolism slows down, almost to a halt, while their body temperature decreases when outside temperature drops near or beyond freezing conditions. Hibernation begins as a result. Frogs and reptiles stop hibernating as soon as their body temperature increases depending on the outside temperature when the weather gets warm. These organisms are called cold blooded animals (with variable body temperatures) because of this feature.

The heart of a crocodile is different to other reptiles in that it has four chambers just like birds and mammals. Blood is sent to the lungs for gas exchange from the right, and from the left ventricle it is pumped to the body. Thus the two types of blood do not mix in the heart. However, what is interesting is that blood is mixed as soon as it leaves the heart via a valve (foramen of panizza) placed in between the right and left aorta.

What could be the purpose of blood, which does not normally mix in the heart, mixing through the medium of a hole? Does this opening in between two aortas indicate a flaw? It is understood after some research that this hole in fact is not a flaw or an anomaly; on the contrary, it is a necessity for a metabolism suited perfectly to the lifestyle of the crocodile.

Warm blooded vertebrates like birds and mammals with a four chamber heart have faster metabolic speeds and higher blood pressures. For these organisms can only supply the energy they consume during their daily activities via such a fast metabolism and a high level of oxygen provided with oxygenated blood.

If the metabolism of a crocodile was fast like mammals all throughout the year, it would have to continuously be nourished and use oxygen. Furthermore, because crocodiles do not have much predators, they could have also lead to the extinctions of some species by overpopulating if they featured a faster metabolism. The low ratio of heart-body mass in crocodiles (0.15%) compared to mammals and birds (0.40%-0.50%) cause the movements of crocodiles to be relatively slower. The Almighty, who creates everything with his wisdom, lowers the blood oxygen ratio and the metabolic speed of crocodiles by creating a valve that combines the two aortas. Thus eliminating the possibility of crocodile overpopulation.

Crocodiles have two aortic arches whereas mammals only have a left, and birds have one right aortic arch. The left aortic arch, despite some contact with the returned blood via foramen of panizza, delivers the oxygenated blood towards intestines, stomach, spleen and the liver after receiving it from the left ventricle of the heart. This is because the digestive system of a crocodile requires oxygen-rich blood. Deoxygenated blood while exiting the right ventricle goes towards the pulmonary arteries of the lung for exchange and mixes with oxygenated blood coming from the right aorta, feeding other organs that are instrumental for its slow metabolism.

Under the water, separated oxygen-rich and oxygen-poor blood mixes when exiting the heart and switches route, thus making oxygenated blood vessels start to carry oxygen poor blood. So what is the reason behind this switch in the direction of the bloodstream under the water? See at this point, the extraordinary features of the crocodile blood circulation system kick in. The two anatomical features belonging only to only crocodile hearts is what enables them to stay under water without breathing. Because of little or no lung use under the water, a big portion of the blood stream is diverted away from lungs; therefore oxygen poor blood is pumped back to the body. As one feature of the two, foramen of panizza restricts (does not close) upon signals coming from nostril sensors under the water but expands and remains open on land. The two aortic arches connects with each other via foramen of panizza as soon as they leave the heart but merge completely in the lower parts of the body away from the heart (anastomosis).

The second feature stems from a serrated valve. Refilling of pumped blood is stopped via a passive, thin leaf-shaped valve which is located at the tip of the pulmonary artery exiting the right ventricle. Thus, one-way direction of blood flow in the heart is maintained. These valves, which carry nodules made of connective tissue, constrict during the dive and blood flow to the lungs is reduced greatly. Therefore blood rejoins the systemic circulation from the right aortic arch.

The blood circulation of crocodiles is similar to birds, mammals, and humans while they are active on land. Oxygen-deprived blood is sent to lungs for gas exchange. The only difference is the turning of the right aorta to the left and the left aorta to the right. Oxygen rich blood not only flows through the left aorta but also through the right aorta via foramen of the panizza as well causing distribution via two channels into the body. However, the foramen of the panizza being open is not sufficient for these two channels to be used. At the same time, the pressure of the blood within the left ventricle needs to be higher as well. This way, high pressure oxygenated blood flows into the right aorta through the opening of the panizza, applying pressure to the valve at the tip of the right aorta to close it in order to prevent the mixing of the oxygen-poor blood into this route. As a result, oxygenated blood gets distributed quickly by each aortic arch without mixing with the used blood. Thus, oxygen-poor and oxygen-rich blood follows the following route on land

* Deoxygenated blood: Body – superior and inferior pulmonary veins – right atrium – right ventricle – lung pulmonary artery – lungs.

* Oxygenated blood: Lung pulmonary vein – left atrium – left ventricle – right aorta and left aorta via panizza valve (both aortas are active) and body.

The opening of the panizza narrows with the help of signals coming from the nostrils when crocodiles submerge. At the same time serrated valves at the tip of pulmonary artery that transports the blood to the lungs also constrict. While this serrated valve is at work, a majority of the blood returning from the body is not sent to the lungs because they are not functioning at the time. This serrated valve also increases the pressure of the right ventricle. This pressure, along with elevated resistance in pulmonary circulation and lowered pressure of systemic circulation, leads to the opening of normal valves at the tip of the left aorta. In the end, the left aorta which normally carries oxygenated blood on land starts carrying oxygen deprived blood, and there is a route switch.

The most beneficial part of this switch is to re-route the deprived blood back to the body via a different route, that is, the left aorta. This by-passes the lungs and prevents time loss. Despite the fact that blood of the left aorta mixes with the oxygenated blood of the right aorta to some degree via the panizza valve, the main function of this opening while submerged is to supply blood flow to the arteries feeding the heart and brain through the transfer of some poor blood from the left aorta into the right aorta; this way vital organs are not left without blood.

Blood returning from the body is not sent to the lungs for gas exchange when crocodiles are under the water. However, existing oxygen in the blood can be delivered to the tissues quickly by a route switch. The amount of bicarbonate ions that is important in the transport of CO2 in the blood increases when oxygen pressure in the tissues drop. Anaerobic respiration of tissues increases. This leads to an increase in lactic acid levels and reduces pH. Eventually, it facilitates the release of oxygen carried by hemoglobin. In the end, oxygen that is bonded with hemoglobin is used more efficiently. In the meantime, the body temperature of a crocodile submerged under water decreases and slows down its metabolism, reducing the need for oxygen. Oxygen stored in the blood can be sufficient up to two hours under the water. However when these reserves are consumed, crocodiles have to resurface to breathe even though it may cost a prey to escape.

Crocodiles can live on land and in the water and adapt to their environments with ease and efficiency thanks to the ponderous working of their mechanisms under water, the change in blood circulation, slow blood flow, reduced body temperature and metabolic speed bestowed upon them. Just like humans in sleep, crocodiles can remain submerged for long periods (4-6 minutes in usual dives; up to 2 hours when pressed) with this perfect system granted to them. Crocodiles use these mechanisms not only when under water, but also while resting or for periods after heavy feeding.

The problem of pulmonary tuberculosis in pregnancy has attracted the attention of doctors for many years and it is still a current issue. Modern researchers and physicians divide tuberculosis into several independent problems which have difficult solutions. On the one hand, there is the influence of tuberculosis on the course of pregnancy and child delivery as well as on the health of a mother and her child. On the other hand, there is the influence of pregnancy and childbirth, the puerperal period and lactation on the course and progress of tuberculosis.

Research on how pregnancy influences the course of tuberculosis has been carried out for many years. Even in the oldest available documents we can find instructions for “personal precautions” and preventative measures against tuberculosis, as well as thoughts about pregnancy and tuberculosis. In 1400 BC the Law of Manu from ancient India prohibited marriages to girls from families with tuberculosis. In different world religions, including Islam and Christianity, there are special restrictions concerning people who suffer from this illness.

In ancient times Hippocrates and Galen taught that pregnancy has a positive influence on the function of lungs. But the Islamic doctors, Arabian as well as Spanish, of the Cordoba Caliphate considered that the blessed process of pregnancy must not be complicated by pulmonary diseases.

With time European medical science changed its point of view. From the second part of the 17th century until the beginning of the 19th century doctors considered that pregnancy had a bad effect on the course of tuberculosis, but then the situation, for some reason, changed. Doctors began to think that pregnancy had a good influence on lung diseases. They even started to advise girls who were susceptible to tuberculosis to marry. Time passed and doctors began to change their opinion on tuberculosis in pregnancy and the extremes in views became less obvious. This happened due to the introduction of an artificial pneumothorax into the treatment of tuberculosis.

Since then the third period in the understanding of the relationship between pregnancy and tuberculosis has begun. The opinion about the course of tuberculosis in pregnant women has changed due to the successful therapy of tuberculosis with the help of the artificial pneumothorax.

During the gestation period, all the organs and tissues of the entire organism experience an increased load, as they are trying to satisfy both their own needs and that of the developing fetus. These morphological and functional changes do not lead to any pathological state in the mother if she is healthy and her course of pregnancy is normal. If the woman’s organism has been weakened by a chronic immunodeficiency due to poor environmental conditions or if she has a tuberculosis process in her organism, then functional changes and tissue dystrophies can develop in her nervous system which will lead to metabolic disorders. Changes in ergasia caused by pregnancy and connected with changes in higher nervous activity, as well as with endocrine reorganization, can influence the development and the course of the tubercular process.

Before penicillin was discovered, pregnancy usually led to the progression of the disease and in many cases even ended fatally. Nowadays due to the use of effective antituberculous medicines the attitude towards possible pregnancy of women who have active tuberculosis has considerably changed.

Tuberculosis in a pregnant woman usually starts in an acute form; at this stage infiltrative forms of the disease with necrogenic and bacterioexcretion prevail, often combined with exudative pleurisy, trachea, larynx and bronchi lesions.

Frequent consecutive pregnancies have a negative effect on the state of women who suffer from tuberculosis; they weaken the organism and can cause the recrudescence of the tuberculosis process. This is very typical of many families in poor Asian and African countries. More than half of all pregnant women suffering from an active form of tuberculosis experience a progressive iron deficiency anemia during the first three months of pregnancy and in the second trimester of pregnancy this can be observed in almost all patients. Malaria is also widespread in Asian and African countries that are situated to the south of Sahara and are the second reason for iron deficiency anemia.

According to modern views, one of the reasons for the recrudescence of the tubercular process during pregnancy is an irregular or non-systematic treatment of this illness or the absence of any treatment at all. The recrudescence of the process observed in those suffering from destructive pulmonary tuberculosis is caused by the severity of the illness itself when new conditions for the organism occur. In this case, pregnancy begins against the background of an advanced chronic immune deficiency. At the same time, due to the feto-placental complex operation, functional changes in the nervous, respiratory, cardiovascular and urinary systems, as well as hormonal changes, in the organism of a pregnant woman take place.

Moreover, the development of the fetal skeleton requires calcium which is absorbed not only via the blood of the mother, but also from the healed niduses of tuberculosis and as a result, the progression of a specific process can appear.

The reactivation of the tubercular process happens due to a decrease in the responsiveness of the organism and because of an increase in the activity of the reproductive hormones and the loosening of the connective tissues which are physiologically involved in pregnancy. The amount of plasma and extra vascular fluid increases. Due to these changes, a swelling and loosening in the inactive tubercular niduses with the mycobacteria of tuberculosis can appear. And loosening, in its turn, enables a lymphohematogenous spread of mycobacteria.

In addition to these, the delivery of a child leads to a speedy reorganization of all the functions of the organism; lactation and nursing in their turn are combined with an increased loss daily of nutritious matters and a large amount of protein and fats. In case of destructive pulmonary tuberculosis, due to the fact that the diaphragm descends (resulting in the abdominal decompression ceasing to have a therapeutic action of pneumoperitoneum) bronchogenic dissemination appears in the unaffected parts of the lungs.

A specific active process can be observed in women belonging to the high-risk group in connection with tuberculosis. The high-risk group combines women who have recently suffered from tuberculosis (less than one year after treatment), those who have just been operated on for a tuberculosis connected illness (less than one year), women with tuberculosis of different localizations younger than 20 years (for Asia and Africa) and those older than 35 years (for Europe and the USA), those with widespread forms of the tubercular process withstanding its stage, women who have had contact with people discharging bacteria or people suffering from tuberculosis but not discharging bacteria, and also those who have coexisting illnesses (diabetes, chronic nonspecific pulmonary illnesses, problems with kidneys, stomach and duodenum ulcer), and also women who use alcohol, narcotics, those who smoke and lead asocial ways of life. In these cases, the women must be properly examined during the gestation period, including X-rays.

Treatment of tuberculosis during pregnancy

All other conditions being equal, the timely detection of active tuberculosis during pregnancy allows doctors to provide a full course of treatment, allowing the woman to recover and give birth to a healthy child. Untreated active tuberculosis of the mother is much more dangerous for the fetus than anti-tuberculosis chemotherapy.

Special attention must be paid to healthy women who are in contact with bacillary patients. Quite often these women might undergo active tuberculosis for the first time during pregnancy or after the delivery itself.

In the pre-penicillin era the recrudescence of the tubercular process during pregnancy and after the delivery proceeded in an acute form with frank infiltrative changes, a necrogenic process, bloody expectoration and very often a generalization of the process. Nowadays, the clinical outlook for complications and the recrudescence of tuberculosis against the background of pregnancy is less gloomy. It more resembles the toxicosis of pregnancy or respiratory diseases.

While examining a patient, special attention must be paid to chest problems like moist or dry coughs, bloody expectoration, pain in the chest and shortness of breath. If the patient coughs with expectoration for 2 weeks then she must be examined for mycobacteria with the usage of a microscopic technique.

Another syndrome, which is also very important, is a complex of intoxication symptoms (weakness, hidrosis, anorexia, weight loss, long-lasting low grade fever and hyperirritability) which need to be detected to discover the reason for their development. While examining the anamnesis of a pregnant woman it is necessary to learn if she has ever suffered from tuberculosis before, if she has had any possible contacts with infected people, whether there are cases of tuberculosis or concomitant diseases in her family as all of these can be very useful for the verification of tuberculosis.

When active pulmonary tuberculosis is suspected an X-ray examination is necessary. When the chest is in frontal projection, the X-ray exposure of the fetus is 10 times lower than that of its mother (with compulsory use of a protective apron). Examination of the cough expectoration for the presence of tubercular mycobacteria is one of the easiest, most effective and informative diagnostic methods.

Chemotherapy, which destroys the tubercle bacillus that spread in the organism, plays a leading role in the variety of methods for tuberculosis treatment. By reducing the population of bacteria, chemotherapy supports the healing process, the dispersion of inflammatory changes, the closing of caverns, the encapsulation of the remaining loci as well as preventing the development of sclerosis. When the patient suffers from tuberculosis, the healing processes are very slow; the first stage of the recovery process of mycobacteria ceases and only after some months, in the case of a successful treatment of tuberculosis, does the healing process finish.

The necessary treatment of pregnant women who suffer from tuberculosis must start as soon as the diagnosis has been made. Chemotherapy implies taking antibacterial medicines (isoniaside, rifampicin, pyrazinamide, ethambutol, ethionamide and etc.) in different combinations. The choice of this or that combination depends on the stage of the disease as well as on any undesirable reactions to the medicines prescribed.

The treatment of tuberculosis (if there are indications) continues during the entire pregnancy and lactation period. In particular, patients with tuberculosis that has been diagnosed during the pregnancy are in need of treatment. When there is a systematic treatment, up to the moment of delivery and in the puerperal period, positive clinicoradiologic dynamics can be observed regarding the specific inflammation (stoppage of bacterioexcretion, closing of caverns, dispersion of loci, infiltration and exudate). Patients who reject treatment during the process of pregnancy suffer from an advancement of the illness.

Transplacental infection of the fetus with tuberculosis almost never occurs, but the baby can be infected from the mother in the puerperal period. There is also a possibility of contamination during delivery, but this is a rare occurrence.. God truly protects the innocent!

Permission to breast feed must be given by a joint resolution of an obstetrician, a pediatrician, and a specialist of tuberculosis taking into account the state of a woman and the form and the stage of the tubercular process. Overall precautionary measures must be taken (a nonbacterial mask of 5-6 layers covering the nose and the mouth, a kerchief covering the head and thoroughly washed hands).

A bacteriological study of the breast milk of women who suffer from tuberculosis shows that typical mycobacteria rarely vegetates (no more than 0.33%). Human milk has the ability to suppress the development of the mycobacteria of tuberculosis. This must be connected with the rich spectrum of ferments, immunoglobulins, cellular elements, macro-phages, the complement system, interferon and other factors of nonspecific protection which human milk contains.

The contraindications for nursing are as follows: tuberculosis of the lactiferous gland, an acute form of tuberculosis, active pulmonary tuberculosis with bacterioexcretion, active tuberculosis of any organs detected at the end of the pregnancy or after the delivery, and recrudescence of tuberculosis during the pregnancy. Children born to such mothers are immediately isolated after their birth and bottle fed, they are vaccinated and stay in the hospital for 6 weeks if possible (the minimum period for compulsory postvaccinal isolation).

Thus the tubercular process in the lungs, especially an active one, will have a negative influence on pregnancy and delivery. Babies born to such mothers belong to a high-risk group as far as the possibility of neonatal pathology and antenatal death of the fetus are regarded. Women with pulmonary tuberculosis must undergo regular consultations with both an obstetrician-gynecologist and a phthisiologist from the very early stages of their pregnancy. They must also receive special treatment until all the signs of active tuberculosis have been eliminated.