Apnea Media Base

The rat: a laboratory model for studies of the diving response.
J Appl Physiol. 2010 Jan 21;
Authors: Panneton WM, Gan Q, Juric R
Underwater submersion in mammals induces an apnea, a parasympathetically-mediated bradycardia, and a sympathetically-mediated peripheral vasoconstriction. These effects are collectively termed the diving response, potentially the most powerful autonomic reflex known. Although these physiological responses are directed by neurons in the brain, the study of the neural control of the diving response has been hampered since: a) it is difficult to study the brains of animals while they are underwater, b) feral marine mammals are usually large and have brains of variable size, and c) there are but few references on the brains of naturally-diving species. Similar responses are elicited in anesthetized rodents after stimulating their nasal mucosa, but this nasopharyngeal reflex has not been compared directly to natural-diving behavior in the rat. In the present study, we compared…

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Facial immersion in cold water enhances cerebral blood velocity during breathhold exercise in humans.
J Appl Physiol. 2009 Jan 29;
Authors: Kjeld T, Pott FC, Secher NH
The diving response is initiated by apnea and facial immersion in cold water and includes, besides bradycardia, peripheral vasoconstriction, while cerebral perfusion may be enhanced. This study evaluated whether facial immersion in 10 degrees C water has an independent influence on cerebral perfusion evaluated as the middle cerebral artery mean flow velocity (MCA Vmean) during exercise in nine male subjects. At rest, a breath-hold of maximum duration increased the arterial carbon dioxide tension (PaCO2) from 4.2 to 6.7 kPa and MCA Vmean from 37 to 103 cm(.)s(-1) mean (~178%; P0.001). Similarly, during 100 W exercise, a breathhold increased PaCO2 from 5.9 to 8.2 kPa (P0.001) and MCA Vmean from 55 to 113 cm(.)s(-1) (~105%) and facial immersion further increased MCA Vmean to 122 cm(.)s(-1) (~88%; both P0.001). MCA Vmean a…

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Repetitive paired stimulation of nasotrigeminal and peripheral chemoreceptor afferents cause progressive potentiation of the diving bradycardia.
Am J Physiol Regul Integr Comp Physiol. 2008 Nov 5;
Authors: Rozloznik M, Paton JF, Dutschmann M
The hallmarks of the mammalian diving response are protective apnea and bradycardia. These cardio-respiratory adaptations can be mimicked by stimulation the trigeminal ethmoidal nerve (EN5) and reflect oxygen conserving mechanisms during breath-hold dives. Increasing drive from peripheral chemoreceptors during sustained dives was reported to enhance the diving bradycardia. The underlying neuronal mechanisms, however, are unknown. In the present study, expression and plasticity of EN5-bradycardias after paired stimulation of the EN5 and peripheral chemoreceptors was investigated in the in situ working heart-brainstem preparation. Paired stimulations enhanced significantly the bradycardic responses compared to EN5-evoked bradycardia using sub-maxim…

To evaluate the separate cardiovascular response to body immersion and increased environmental pressure during diving, 12 healthy male subjects (mean age 35.2 6.5), underwent 2D-Doppler Echocardiography in 5 different conditions: out of water (BASAL); he

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1. Short-term cardiovascular effects of partial and total immersion of eighteen human subjects in the horizontal plane have been examined. Brachial arterial pressure, heart rate, forearm blood flow and respiratory movements were monitored simultaneously throughout the experiments. Forearm vascular resistance was calculated from the mean blood pressure and mean flow.2. Total immersion, including the face, with breath-holding resulted in a 61 /- 43ncrease in forearm vascular resistance with an associated 29 /- 15eduction in forearm blood flow. The concurrent bradycardia was significantly different from the heart rate changes during breath-holding with the torso only immersed, or during total immersion with snorkel-breathing. Neither breath-holding in air or with only the torso immersed, nor total immersion with snorkel-breathing produced such a diving response.3. Breath-holding, after several minutes of total immersion and snorkel-breathing, produced an attenuated diving response. It ther

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Peripheral receptors signalling in both the 3 main divisions of the trigeminal nerves and in the glossopharyngeal nerves are most likely involved in the onset of the apnea in diving ducks. Since the response also takes place when ducks are submerged in mercury, these peripheral receptors are hardly specific to water. Neither any of the 3 main groups of trigeminal, nor the glossopharyngeal receptors are alone responsible for the initiation of the apnea. Most likely the apnea takes place when the total impact on the 'respiratory centre' in the brain exceeds a certain treshold value, due to activation of a certain number of both trigeminal and glossopharyngeal peripheral receptors. However, even very local stimulation of the glottal area invariably evoked apnea, indicating a higher density of receptors there than for example on the beak or in the nares. This idea is supported by the fact that not even heavy rain evokes any response at all. It is unlikely that the cardiovascular adjustments display

The steady-state ventilatory responses to hypercapnia and hypoxia in 7 assisted breath-hold divers (Funado) were compared with those in 7 normal sedentary controls. Ventilatory response to hypercapnia was measured from the slope of the hyperoxic VN-PETCO2 line, where VN was normalized minute ventilation using the allometric coefficient and PETCO2 end-Tidal PCO2. The slope of this line in the Funado (1.48 /- 0.54 liters . min-1 . Torr-1) was significantly less than in the control (2.70 /- 1.08 liters . min-1 . Torr-1) (p less than 0.025). On the other hand, hypoxic sensitivity estimated by hyperbolic and exponential mathematical equations was not found to be significantly different between the two groups, although estimated increments in ventilation using the hyperbolic equation exhibited significantly lower response in the Funado than in the control only when PETO2 decreased lower than 50 Torr (p less than 0.05). These findings in the Funado were different from our previous observations obtai

We have investigated the possibility that a bronchoconstriction accompanies the vagally-mediated bradycardia induced in man by immersion of the face in cold water. Forced expiratory flows (FEF) at 40
nd 25f vital capacity (VC) have been measured from partial flow-volume curves obtained during forced expirations starting at 70C. These were performed immediately after 15 s apnoea with or without face immersion, and compared with control expirations having the same volume history but without the preceding apnoea. Five of the 10 subjects showed evidence of a greater than 10eduction in FEF, which averaged 17�Fig. 2). Half the response was attributable to the apnoea alone and the other half, which was abolished by ipratropium, to cold face immersion (Fig. 3). This bronchoconstriction appears to be a new component of the 'diving response' in man, mediated, like the bradycardia, by vagal efferents.
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We have found that the stimulation of the mucosa of the rhinopharynx elicits apnea and bradycardia in the duck. This appears to be the most important area involved in the production of diving responses. The laryngeal mucosa and other areas, as the external nares, were found to be of lesser relevance. We have also observed that visual and thermal stimuli may participate in the elicitation of the responses to submersion.
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Multi-unit recordings of muscle-nerve sympathetic activity (m.s.a) or skin-nerve sympathetic activity (s.s.a) were made in the left peroneal nerve of sixteen healthy volunteers during simulated diving by immersion of the face in a tub of water. The procedure was varied by the use of different water temperatures, by diving with snorkel breathing, by apnoea without diving, and by apnoea with a stream of air against the face instead of immersion in water. Diving for 12 s elicited a pronounced activation of m.s.a., the mean increase from control periods being 360�The response was stronger with lower water temperatures. Immersion of the whole face evoked a stronger increase in m.s.a. than immersion of mouth and nose only. Diving without apnoea elicited a significant but weaker increase in m.s.a., whereas apnoea only for 12 s did not influence the sympathetic outflow. Cool air against the face during apnoea for 12 s was associated with a significant increase in m.s.a. The increase in m.s.a. usually

The diving reflex is a complex cardiovascular-respiratory response to immersion. This multireflex response in animals consists of apnea; bradycardia (the experimental parameter most often measured); peripheral vasoconstriction (resulting in preferential perfusion of the brain and heart); decreased cardiac output (with a maintained or increased stroke volume); and an increase in mean arterial blood pressure. These cardiovascular alterations act in a manner that conserves oxygen for the heart and brain. Because alcohol is often involved in water accidents with associated submersions, these initial experiments dealt with human volunteers who consumed alcohol to a blood level of 0.1 g�legal level of intoxication). The diving reflex was elicited before and after alcohol consumption. Heart rate, blood pressure, and cardiac output were measured before, during, and after face immersion in 4 C water. In the sober state, immersion decreased heart rate, increased stroke volume, increased blood pressure,