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PubMed2003

Regional heterothermy and conservation of core temperature in emperor penguins diving under sea ice.

Temperatures were recorded at several body sites in emperor penguins (Aptenodytes forsteri) diving at an isolated dive hole in order to document temperature profiles during diving and to evaluate the role of hypothermia in this well-studied model of penguin diving physiology. Grand mean temperatures (+/-S.E.) in central body sites during dives were: stomach: 37.1+/-0.2 degrees C (n=101 dives in five birds), pectoral muscle: 37.8+/-0.1 degrees C (n=71 dives in three birds) and axillary/brachial veins: 37.9+/-0.1 degrees C (n=97 dives in three birds). Mean diving temperature and duration correlated negatively at only one site in one bird (femoral vein, r=-0.59, P<0.05; range <1 degrees C). In contrast, grand mean temperatures in the wing vein, foot vein and lumbar subcutaneous tissue during dives were 7.6+/-0.7 degrees C (n=157 dives in three birds), 20.2+/-1.2 degrees C (n=69 in three birds) and 35.2+/-0.2 degrees C (n=261 in six birds), respectively. Mean limb temperature during dives negatively correlated with diving duration in all six birds (r=-0.29 to -0.60, P<0.05). In two of six birds, mean diving subcutaneous temperature negatively correlated with diving duration (r=-0.49 and -0.78, P<0.05). Sub-feather temperatures decreased from 31 to 35 degrees C during rest periods to a grand mean of 15.0+/-0.7 degrees C during 68 dives of three birds; mean diving temperature and duration correlated negatively in one bird (r=-0.42, P<0.05). In general, pectoral, deep venous and even stomach temperatures during diving reflected previously measured vena caval temperatures of 37-39 degrees C more closely than the anterior abdominal temperatures (19-30 degrees C) recently recorded in diving emperors. Although prey ingestion can result in cooling in the stomach, these findings and the lack of negative correlations between internal temperatures and diving duration do not support a role for hypothermia-induced metabolic suppression of the abdominal organs as a mechanism of extension of aerobic dive time in emperor penguins diving at the isolated dive hole. Such high temperatures within the body and the observed decreases in limb, anterior abdomen, subcutaneous and sub-feather temperatures are consistent with preservation of core temperature and cooling of an outer body shell secondary to peripheral vasoconstriction, decreased insulation of the feather layer, and conductive/convective heat loss to the water environment during the diving of these emperor penguins.

Animals↗
PubMed2001

The effects of depth on the cardiac and behavioural responses of double-crested cormorants (Phalacrocorax auritus) during voluntary diving.

Heart rate and dive behaviour were monitored in double-crested cormorants (Phalacrocorax auritus) during shallow (1 m) and deep diving (12 m), after breathing different gas mixtures, to investigate the role of depth and the accompanying changes in blood gas levels in cardiac and behavioural control during voluntary diving. Pre-dive heart rate in both shallow- and deep-diving birds was approximately three times the resting heart rate (137.9+/-17.5 beats min(-1); mean +/- S.D., N=5), falling abruptly upon submersion to around 200-250 beats min(-1). During shallow diving, the initial reduction in heart rate was followed by a secondary, more gradual decline, to around the resting level. In contrast, during deep diving, heart rate stabilised at 200-250 beats min(-1). In dives of similar duration, mean dive heart rate was significantly lower during shallow diving (163.2+/-14.0 beats min(-1)) than during deep diving (216.4+/-7.7 beats min(-1)), but in both cases was significantly above the resting value. The difference in cardiac response is probably due to an increase in arterial oxygen tension (Pa(O(2))) during the descent phase of deep dives (compression hyperoxia). Exposure to a hyperoxic gas mixture before shallow diving significantly increased mean dive heart rate, while exposure to a hypoxic gas mixture in both the shallow and deep dive tanks significantly reduced mean dive heart rate. In contrast, breathing hypercapnic gas before diving had no significant effect on dive heart rate. We suggest that the cardiac response to voluntary diving in double-crested cormorants is strongly influenced by changes in blood oxygen levels throughout the dive. Dive duration was unaffected by alterations in inspired gas composition, but surface interval duration decreased during hyperoxic gas exposure and increased during hypoxic gas exposure. The most efficient dive pattern (highest dive/pause ratio) was observed after hyperoxic exposure. Our study suggests that blood oxygen level is a powerful stimulus that facilitates the cardiac and behavioural adjustments during foraging that are important components of a strategy allowing double-crested cormorants to maximise the time spent under water and, hence, potential foraging time.

Animals↗
PubMed2003

Energetics of diving in macaroni penguins.

Heart rate (fH), abdominal temperature (T(ab)) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V(O(2))) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V(O(2)) was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147+/-6 beats min(-1). When this fH is used to estimate (O(2)) of 26.2+/-1.4 ml min(-1) kg(-1) then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in T(ab) during a diving bout was 2.32+/-0.2 degrees C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as T(ab) declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than T(ab) are important in determining the duration of dives and dive bouts. Lowered T(ab) will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.

Aerobiosis↗
PubMed1994

Diving pattern of fishermen in the Pescadores.

Professional diving fishermen in the Pescadores Archipelago (119.30 degrees W, 23.30 degrees N) dive with a simple hookah system. Although they use modern equipment, such as wet suit, face mask, mouth piece with demand valve, spear gun, weight belt, and fins, their lack of knowledge of diving medicine is apparent. On the average, 180 cases of decompression sickness (DCS) per year were reported to occur in the Pescadores. We conducted studies in 1990 and 1992 on three islands of the Archipelago. At the time of our study, an estimated 140 diving fishermen resided on these three islands. Of the 62 fishermen interviewed, 14 volunteered for the recording of dive profiles using a diver-carried data logger. In the summer of 1990, a group of eight fishermen dived, on the average, to a depth of 17.8 +/- 5.3 m (mean +/- SD; range, 8-27 m) for 26.9 +/- 19.7 min (5-66 min). Although the diving depth was similar to that of the average recollections of 43 divers, 20.1 +/- 4.4 m (15-30 m), the actual diving time was far shorter than that of their recollections, 426 +/- 138 min (240-630 min). The post-typhoon sea floor conditions may have shortened their diving time. In the summer of 1992, a group of six fishermen dived to 20.5 +/- 3.8 m (15-26 m) for 56.4 +/- 21.2 min (18-84 min). Again, the diving depth matched that of their recollection well, 22.2 +/- 2.5 m (20-26 m), but their bottom time was far shorter than they believed, 270 +/- 108 min (120-480 min). They used no decompression procedures, regardless of the bottom time and diving depth. In the 1990 group, 5 out of 10 equivalent single dive bottom times (ESDBT) exceeded U.S. Navy no-decompression (No-D) air dive limits; whereas in the 1992 group, 7 out of 9 ESDBTs exceeded No-D limits. Eight of the 38 discrete dives exceeded the No-D limits, even if we underestimate their decompression stress by disregarding their repetitive dive history. However, no symptoms of DCS were observed in either the 1990 or 1992 groups of 14 divers, despite 63% of the ESDBTs and 21% of discrete dives having exceeded the No-D limits. Adaptation to diving work may have allowed them to exceed the established No-D limits. The existing records of incidence of DCS from this region suggest that previously they must have dived longer or deeper or both during times of abundant resources.

Adult↗
PubMed1988

Chemoreceptor control of heart rate and behaviour during diving in the tufted duck (Aythya fuligula).

1. The role of chemoreceptors in the control of heart rate and behaviour during diving activity in the tufted duck was investigated in two ways. In a closed-loop experiment, ducks were exposed to ambient gas mixtures of varied composition during diving activity in an indoor tank. Characteristics of diving behaviour, heart rate and deep body temperature were monitored under hypoxic, hyperoxic and hypercapnic conditions and compared with those in air. Secondly, in an open-loop experiment the role of the carotid body (CB) chemoreceptors in the control of the responses to altered inspired gas composition and in the cardiac responses to extended and enclosed dives (Stephenson, Butler & Woakes, 1986) was investigated by chronic bilateral denervation of these receptors. 2. Heart rate during submersion was unaffected by inspired gas composition in control (data from intact and sham-operated ducks combined) and CB-denervated ducks, though diving behaviour was significantly modified in both groups of animals in response to altered inspired gas composition. Hypoxia and hypercapnia resulted in an increase in the proportion of total diving time spent breathing at the surface. The main effect of hypoxia (9-10% O2) was to reduce dive duration in control ducks and this effect was almost completely abolished after CB denervation. Hypercapnia (5-6% CO2) reduced dive duration less markedly than hypoxia but it greatly increased the duration of the inter-dive interval, effects which were not significantly influenced by CB denervation. Hyperoxia (40-45% O2) had very little effect on either behaviour or heart rate during diving, although deep body temperature was significantly elevated in this gas mixture during diving activity. There was also a less marked, but nevertheless significant, apparent hyperthermia during diving activity in air on an indoor tank but not on an outdoor pond. Conversely, there was a significant apparent hypothermia during diving activity under hypoxic conditions. 3. The CB chemoreceptors were shown to play a role in cardiac control during diving under certain circumstances. The duration of pre-dive tachycardia was significantly increased in hypoxia and this increase was abolished after CB denervation. The rate of development of bradycardia during extended and enclosed dives was slowed following CB denervation, though the initiation of the responses in extended and enclosed dives and the eventual attainment of sub-resting heart rates in enclosed dives were not prevented, indicating that other, as yet unidentified, sensory inputs are involved in cardiac control under these conditions.

Animals↗
PubMed1993

[Experimental studies of the effects of enriched air nitrox dive on shortening of decompression time and reduction of risks of decompression sickness].

Enriched air nitrox diving has been conducted to shorten decompression time as well as to reduce risks of decompression sickness. Nine volunteer divers served as subjects for nitrox (-a: 60% N2 and 40% O2, and -b: 67.5% N2 and 32.5% O2) and air chamber dives of 20 m/60 min, 30 m/60 min and 40 m/60 min. Venous gas emboli (VGE) were examined after surfacing in a series of nitrox dives and of air dives to compare the risks of decompression sickness (DCS). Three divers as a group were compressed in a chamber for each dive. Decompression was carried out according to the Norwegian Navy nitrox decompression tables for the nitrox dives, and for the air dives the Japanese Ministry of Labor tables were used. Decompression time was much shorter in nitrox diving than in air dives for the same dive profiles. All of nitrox-a and air divers showed no VGE nor DCS symptoms after surfacing of 20 m dives. In case of 30 m dives, VGE appeared in one diver (33%) without DCS symptoms in nitrox-a dive but no VGE nor DCS in nitrox-b dive, whereas for the same air dives two subjects (66%) had VGE and DCS symptoms. When the depth was increased to 40 m in the nitrox dive, nitrox-b did not show both VGE and DCS, while the air dive showed one VGE and one DCS. These results suggest that the nitrox dive with suitable decompression schedule reduces the risks of DCS as well as shortening decompression obligation.

Adult↗
PubMed1998

Avian diving, respiratory physiology and the marginal value theorem.

Behavioural studies of diving birds have reported that the ratio of dive duration to the duration of the subsequent period on the surface displays a characteristic relation to dive duration. For short dives, the dive to surface ratio increases with dive duration, whereafter the relation peaks, and for longer dives decreases with increasing dive duration. Such a relationship is not a general prediction of existing marginal value models which have been used to predict optimal diving behaviour. This may be because the smooth curve used to describe the oxygen gain rate of individuals after surfacing is not a good reflection of the respiratory physiology of birds. Here we argue that on physiological grounds, the oxygen gain curve for avian divers will not be smooth, but will have two distinct regions (representing oxygen recovery in the respiratory tract, and in haemoglobin and myoglobin, respectively). Modifying two of the classical diving models by incorporating such a kinked curve causes them to predict the humped relationship between dive to surface ratio and dive duration under many circumstances. We also present data on the duration of dives and surface periods from three species of diving seabirds: the shag, Phalacrocorax aristotelis, the black guillemot, Cepphus grylle and the common guillemot, Uria aalge. All three species showed a humped relationship for dive to surface ratio as a function of dive duration. In line with the predictions of our model, when oxygen stores on surfacing were greatly depleted, the dive to surface ratio peaked at short dive durations. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Characteristics of 'low risk' and 'high risk' dives by young adults: risk reduction in spinal cord injury.

STUDY DESIGN: To establish benchmark normative data for dive entries performed by young adults of the age range most likely to sustain a diving spinal cord injury. Data acquired from analysis of the dives performed, along with survey information, were used to determine which factors make the most contribution to the level of risk in diving. OBJECTIVES: To identify influential variables which could contribute to risk of spinal cord injury for each of four types of dives. The types of dives investigated were: dive entries from deck level to tread water (Treadwater); deck level to swim 25 m (Deck); starting block height to swim 25 m (Block); and a running dive entry to swim 25 m (Running). SETTING: Victoria, Australia. METHODS: Ninety-five first year university students (average age 19.9 years) performed three or four dives which were video-recorded for later analysis. Maximum depth reached was used as an indicator of risk, and velocity at maximum depth, distance at maximum depth, angle of entry and flight distance were measured for each dive. Participants also completed a questionnaire designed to elicit information about their swimming and diving background. Unlike previous diving studies, participants were recreational rather than competitive swimmers. They were not aware that the dive was the focal point, assuming that the researchers were investigating their swimming and treadwater ability. RESULTS: A stepwise multiple regression was applied to predict depth for each dive condition, and demonstrated that four variables were able to account for 56% of the variance for Treadwater, 68% for Deck; 73% for Running and 79% for Block. In all conditions involving swimming after the dive (ie Deck, Block and Running), beta weights showed that distance at maximum depth had the greatest influence on the depth of a dive. Flight distance and angle of entry were the next most influential variables. For the Treadwater condition, beta weights showed angle of entry was the most influential variable, followed by velocity at maximum depth, distance at maximum depth and swim rank. CONCLUSION: It is recommended that divers strive to surface in as short a distance as possible by maximising flight distance and aiming for a low entry angle. Implementation of steering-up techniques will assist in minimising dive depth.

Adult↗
PubMed2005

Air sac PO2 and oxygen depletion during dives of emperor penguins.

In order to determine the rate and magnitude of respiratory O2 depletion during dives of emperor penguins (Aptenodytes forsteri), air sac O2 partial pressure (PO2) was recorded in 73 dives of four birds at an isolated dive hole. These results were evaluated with respect to hypoxic tolerance, the aerobic dive limit (ADL; dive duration beyond which there is post-dive lactate accumulation) and previously measured field metabolic rates (FMRs). 55% of dives were greater in duration than the previously measured 5.6-min ADL. PO2 and depth profiles revealed compression hyperoxia and gradual O2 depletion during dives. 42% of final PO2s during the dives (recorded during the last 15 s of ascent) were <20 mmHg (<2.7 kPa). Assuming that the measured air sac PO2 is representative of the entire respiratory system, this implies remarkable hypoxic tolerance in emperors. In dives of durations greater than the ADL, the calculated end-of-dive air sac O2 fraction was <4%. The respiratory O2 store depletion rate of an entire dive, based on the change in O2 fraction during a dive and previously measured diving respiratory volume, ranged from 1 to 5 ml O2 kg(-1) min(-1) and decreased exponentially with diving duration. The mean value, 2.1+/-0.8 ml O2 kg(-1) min(-1), was (1) 19-42% of previously measured respiratory O(2) depletion rates during forced submersions and simulated dives, (2) approximately one-third of the predicted total body resting metabolic rate and (3) approximately 10% of the measured FMR. These findings are consistent with a low total body metabolic rate during the dive.

Animals↗
PubMed2006

The effects of depth, temperature and food ingestion on the foraging energetics of a diving endotherm, the double-crested cormorant (Phalacrocorax auritus).

Avian divers are confronted with a number of physiological challenges when foraging in cold water, especially at depth. Besides the obvious constraint imposed by the necessity to return to the surface for gas exchange, cold water temperatures and a reduction in body insulation due to the increase in pressure with dive depth will elevate the energetic costs of foraging in these endotherm divers. The complex effect that depth has on the diving energetics of aquatic birds has largely been ignored. To date, no study has assessed the impact of depth on diving energetics over a significant depth range, naturally encountered by the diver. We used open-circuit respirometry to study the energetic requirements of a foot-propelled pursuit diver, the double-crested cormorant (Phalacrocorax auritus albociliatus), when diving in a shallow (1 m) and deep (10 m) dive tank and when resting in air and water. We also investigated the modifying effects of air or water temperature and feeding status on the costs associated with diving and resting. Of all factors investigated, dive depth exercised the strongest influence on diving metabolic rate. Diving to 10 m depth increased metabolic rate on average by 22% when compared with shallow diving. Declining temperatures in air and water significantly elevated metabolic rate of cormorants resting in air and water as well as during diving. Feeding before resting in water or diving increased metabolic rate by 5-8% for at least 2 h. Cormorants maintained an elevated stomach temperature (>42 degrees C) when resting in water and during diving, even at cold temperatures. The elevated dive costs during deep diving, when compared with shallow diving, are most likely a consequence of the increased thermoregulatory costs associated with a greater heat loss to the water at depth. Nevertheless, our study shows that dive costs in double-crested cormorants are similar to those of other foot-propelled avian divers.

Animals↗