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PubMed2006

The influence of body size on the diving behaviour and physiology of the bimodally respiring turtle, Elseya albagula.

In aquatic vertebrates that acquire oxygen aerially dive duration scales positively with body mass, i.e. larger animals can dive for longer periods, however in bimodally respiring animals the relationship between dive duration and body mass is unclear. In this study we investigated the relationships between body size, aquatic respiration, and dive duration in the bimodally respiring turtle, Elseya albagula. Under normoxic conditions, dive duration was found to be independent of body mass. The dive durations of smaller turtles were equivalent to that of larger individuals despite their relatively smaller oxygen stores and higher mass specific metabolic rates. Smaller turtles were able to increase their dive duration through the use of aquatic respiration. Smaller turtles had a relatively higher cloacal bursae surface area than larger turtles, which allowed them to extract a relatively larger amount of oxygen from the water. By removing the ability to respire aquatically (hypoxic conditions), the dive duration of the smaller turtles significantly decreased restoring the normal positive relationship between body size and dive duration that is seen in other air-breathing vertebrates.

Animals↗
PubMed2001

Extreme human breath-hold diving.

In this paper, the respiratory, circulatory and metabolic adjustments to human extreme breath-hold diving are reviewed. A survey of the literature reveals that in extreme divers, adaptive mechanisms take place that allow prolongation of apnoea beyond the limits attained by non-diving subjects, and preservation of oxygen stores during the dives. The occurrence of a diving response, including peripheral vasoconstriction, increased arterial blood pressure, bradycardia and lowered cardiac output, is strongly implicated. Some peripheral regions may be excluded from perfusion, with consequent reliance on anaerobic metabolism. In addition, extreme breath-hold divers show a blunted ventilatory response to carbon dioxide breathing, possibly as a consequence of frequent exposure to high carbon dioxide partial pressures during the dives. These mechanisms allow the attainment of particularly low alveolar oxygen (< 30 mmHg) and high alveolar carbon dioxide (> 50 mmHg) partial pressures at the end of maximal dry breath-holds, and reduce oxygen consumption during the dive at the expense of increased anaerobic glycolysis (rate of blood lactate accumulation > 0.04 mM.s-1). The current absolute world record for depth in breath-hold diving is 150 m. Its further improvement depends upon how far the equilibrium between starting oxygen stores, the overall rate of energy expenditure, the fraction of energy provided by anaerobic metabolism and the diving speed can be pushed, with consciousness upon emersion. The ultimate limit to breath-hold diving records may indeed be imposed by an energetic constraint.

Adaptation, Physiological↗
PubMed2006

Optimal diving behaviour and respiratory gas exchange in birds.

This review discusses the advancements in our understanding of the physiology and behaviour of avian diving that have been underpinned by optimal foraging theory and the testing of optimal models. To maximise their foraging efficiency during foraging periods, diving birds must balance numerous factors that are directly or indirectly related to the replenishment of the oxygen stores and the removal of excess carbon dioxide. These include (1) the time spent underwater (which diminishes the oxygen supply, increases carbon dioxide levels and may even include a build up of lactate due to anaerobic metabolism), (2) the time spent at the surface recovering from the previous dive and preparing for the next (including reloading their oxygen supply, decreasing their carbon dioxide levels and possibly also metabolising lactate) and (3) the trade-off between maximising oxygen reserves for consumption underwater by taking in more air to the respiratory system, and minimising the energy costs of positive buoyancy caused by this air, to maximise the time available underwater to forage. Due to its importance in avian diving, replenishment of the oxygen stores has become integral to models of optimal diving, which predict the time budgeting of animals foraging underwater. While many of these models have been examined qualitatively, such tests of predictive trends appear fallible and only quantifiable support affords strong evidence of their predictive value. This review describes how the quantification of certain optimal diving models, using tufted ducks, indeed demonstrates some predictive success. This suggests that replenishment of the oxygen stores and removal of excess carbon dioxide have significant influences on the duration of the surface period between dives. Nevertheless, present models are too simplistic to be robust predictors of diving behaviour for individual animals and it is proposed that they require refinement through the incorporation of other variables that also influence diving behaviour such as, perhaps, prey density and predator avoidance.

Animals↗
PubMed2006

The evolution of a physiological system: the pulmonary surfactant system in diving mammals.

Pulmonary surfactant lines the alveolar air-water interface, varying surface tension with lung volume to increase compliance and prevent adhesion of respiratory surfaces. We examined whether the surfactant system of diving mammals exhibits adaptations for more efficient lung function during diving, to complement other respiratory adaptations. Here we review adaptations at the molecular, compositional, functional and cellular levels and during development for animals beginning life on land and progressing to an aquatic environment. Molecular adaptations to diving were examined in surfactant protein C (SP-C) from terrestrial, semi-aquatic and diving mammals using phylogenetic analyses. Diving species exhibited sites under positive selection in the polar N-terminal domain. These amino acid substitutions may lead to stronger binding of SP-C to the phospholipid film and increased adsorption to the air-liquid interface. The concentration of shorter chain phospholipid molecular species was greater and SP-B levels were lower in diving than terrestrial mammals. This may lead to a greater fluidity and explain the relatively poor surface activity of diving mammal surfactant. There were no consistent differences in cholesterol between diving and terrestrial mammals. Surfactant from newborn California sea lions was similar to that of terrestrial mammals. Secretory activity of alveolar type II epithelial cells of sea lions demonstrated an insensitivity to pressure relative to sheep cells. The poor surface activity of diving mammal surfactant is consistent with the hypothesis that it has an anti-adhesive function that develops after the first entry into the water, with a surfactant film that is better suited to repeated collapse and respreading.

Adaptation, Physiological↗
PubMed2003

Diving emergencies.

Self-Contained Underwater Breathing Apparatus (SCUBA) diving popularity is increasing tremendously, reaching a total of 9 million people in the US during 2001, and 50,000 in the UK in 1985. Over the past 10 years, new advances, equipment improvements, and improved diver education have made SCUBA diving safer and more enjoyable. Most diving injuries are related to the behaviour of the gases and pressure changes during descent and ascent. The four main pathologies in diving medicine include: barotrauma (sinus, otic, and pulmonary); decompression illness (DCI); pulmonary edema and pharmacological; and toxic effects of increased partial pressures of gases. The clinical manifestations of a diving injury may be seen during a dive or up to 24 h after it. Physicians living far away from diving places are not excluded from the possibility of encountering diver-injured patients and therefore need to be aware of these injuries. This article reviews some of the principles of diving and pathophysiology of diving injuries as well as the acute treatment, and further management of these patients.

Adrenal Cortex Hormones↗
PubMed2001

Aerobic dive limit: how often does it occur in nature?

Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is its aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella, the Australian sea lion, Neophoca cinerea, and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.4 times longer than the cADL, while New Zealand sea lions on average dove 1.5 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL (P<0.01, r(2)=0.54). Australian and New Zealand sea lions with longer bottom times also exceeded the cADL to a greater degree. The two sea lions forage on the benthos while the fur seals feed shallow in the water column. It appears that benthic foraging requires these animals to reach or exceed their aerobic dive limit.

Animals↗
PubMed2001

Respiratory effects of a single dive to 50 meters in sport divers with asymptomatic respiratory atopy.

Increasing popularity of sports diving makes it likely that subjects with allergic respiratory diseases will be involved in diving with self contained underwater breathing apparatus (scuba). The present study evaluated the effects of a single scuba-dive on pulmonary function in subjects with respiratory atopy. Specific airways conductance (sGaw), residual volume (RV), forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), mid expiratory flow at 50% of FVC (MEF50), and transfer factor for carbon monoxide (TLCO) were measured in 9 sport divers with a history of hay fever and 9 matched healthy sport divers (control) before, 3 hours and 24 hours after a wet hyperbaric chamber dive to a depth of 50 m. Airway hyperresponsiveness (AHR) was assessed by methacholine challenge 4 weeks after the dive. Atopic subjects and controls did not differ with respect to anthropometric data, diving experience, and predive lung function. A 3% reduction in FVC was found 24h after the dive (p < 0.05) in both groups, whereas sGaw decreased by 15% 24 h after the dive (p < 0.05) in the subjects with respiratory atopy only. Postdive changes in RV, FEV1, MEF50, and TLCO did not reach level of statistical significance. AHR was obtained in 8/9 subjects with respiratory atopy. We conclude that subjects with atopic sensitization and asymptomatic AHR may be more susceptible to effects of diving on pulmonary function.

Adult↗
PubMed2003

Technique and timing in women's inward two and one half somersault tuck (405C) and the men's inward two and one half somersault pike (405B) 3 m springboard dives.

The purpose of this study was to compare the inward two and one half somersault dive in a tuck position (405C) performed by females (n = 22) and the inward two and one half somersault dive in a pike position (405B) performed by males (n = 24) to determine changes required by females to successfully perform 405B. Key performance variables in inward dives were also compared to those of backward dives. Video data of the dives performed at the 1999 FINA World Diving Cup were captured and digitized to obtain times and postures of the divers at specific events including takeoff and entry. Estimates of flight height and mass-normalised work done on the springboard were obtained from flight times. Some females worked the springboard strongly enough to generate sufficient height and rotation to perform 405B. Males performed 405B comfortably because they achieved better height and rotation than the females. A comparison of backward and inward dives revealed that divers are able to attain greater height in backward dives than inward dives.

Analysis of Variance↗
PubMed2005

Breathing hypoxic gas affects the physiology as well as the diving behaviour of tufted ducks.

We measured the effects of exposure to hypoxia (15% and 11% oxygen) and hypercapnia (up to 4.5% carbon dioxide) on rates of respiratory gas exchange both between and during dives in tufted ducks, Aythya fuligula, to investigate to what extent these may explain changes in diving behaviour. As found in previous studies, the ducks decreased dive duration (t(d)) and increased surface duration when diving from a hypoxic or hypercapnic gas mix. In the hypercapnic conditions, oxygen consumption during the dive cycle was not affected. Oxygen uptake between dives was reduced by only 17% when breathing a hypoxic gas mix of 11% oxygen. However, estimates of the rate of oxygen metabolism during the foraging periods of dives decreased nearly threefold in 11% oxygen. Given that tufted ducks normally dive well within their aerobic dive limits and that they significantly reduced their t(d) during hypoxia, it is not at all clear why they make this physiological adjustment.

Animals↗
PubMed1996

Medical aspects of sport diving.

Medical issues in sport diving include illnesses that are caused by diving, and medical disorders that compromise safety. Cerebral air embolism and decompression sickness of the brain and spinal cord can result from diving. Sport divers may manifest a spectrum of symptoms from air embolism, which can range from unconsciousness to minimal symptoms, which include fatigue, personality change, poor concentration, irritability, and changes in vision. The physician must search for these minor symptoms in divers who are suspected of pulmonary barotrauma. Medical disorders of concern in diving include diseases of the lungs, the heart, the brain, and the endocrine system, particularly diabetes. Other factors involved in diving safety are exercise capacity and training. Clinical practice standards usually prohibit diving by individuals who have a seizure disorder that requires continuous medication. In the United States, we will not approve diving for individuals who have insulin-dependent diabetes or severe asthma. Some divers can return to diving after myocardial infarction or bypass surgery if they demonstrate good exercise tolerance and no ischemia on a graded exercise test, which simulates the physical activity needed for safe diving.

Asthma↗
PubMed2005

Recompression treatment of Red Sea diving accidents: a 23-year summary.

OBJECTIVE: The growing popularity of diving sport has resulted in more diving accidents. Our objective was to characterize Red Sea divers requiring recompression treatment in Eilat, to recognize 23-year trends of diving accidents, and to facilitate appropriate administrative and treatment tools for diving accident in this area. DESIGN: Retrospective, uncontrolled study. SETTING: Recompression unit at a Red Sea medical center. PATIENTS: Charts of all divers treated at Eilat's recompression chamber from October 1976 to December 1999 were reviewed. INTERVENTIONS: Recompression treatment. RESULTS: During this period, annual crude numbers increased 5-fold, and a total of 453 patients were treated. Of them, 68% were Israelis and 32% tourists; 76% were males and 23% females; and 21.6% were diving buddies of injured divers (omitted decompression). The mean diving depth causing the accident was 30.2 +/- 13.1 m, and >50% of accidents occurred between 11 and 30 m. Over 42% suffered from decompression sickness (DCS) type 2, 26% from DCS type 1, and 7% from barotraumas. Women, unlike men, presented predominantly DCS type 2 (54% vs. 39%; P = 0.01) and sustained DCS at shallower waters (25.2 +/- 9.1 m) than men (31.8 +/- 13.8 m; P < 0.0001). Primarily, treatment followed recompression in alternating cycles of oxygen and air as stipulated in US Navy Tables 5 (18.1%) and 6 (37.5%). The 48-hour case fatality rate was 0.09%. CONCLUSIONS: This large survey of open sea diving accidents accentuated the need for a national registry of diving accidents and a national database of diving activities.

Adult↗
PubMed2001

Effect of immersion, submersion, and scuba diving on heart rate variability.

BACKGROUND: Heart rate variability (HRV) describes the cyclic variations in heart rate and offers a non-invasive tool for investigating the modulatory effects of neural mechanisms elicited by the autonomic nervous system on intrinsic heart rate. OBJECTIVE: To introduce the HRV concept to healthy volunteers under control conditions and during scuba diving. In contrast with more established manoeuvres, diving probably activates both the sympathetic and parasympathetic nervous system through various stimuli-for example, through cardiac stretch receptors, respiration pattern, psychological stress, and diving reflex. A further aim of the study was to introduce a measure for determining a candidate's ability to scuba dive by providing (a) standard values for HRV measures (three from the time domain and three from the frequency domain) and (b) physiological responses to a strenuous manoeuvre such as scuba diving. METHODS: Twenty five trained scuba divers were investigated while diving under pool conditions (27 degrees C) after the effects of head out immersion and submersion on HRV had been studied. RESULTS AND CONCLUSIONS: (a) Immersion under pool conditions is a powerful stimulus for both the sympathetic and parasympathetic nervous system. (b) As neither the heart rate nor the HRV changed on going from immersion to submersion, the parasympathetic activation was probably due to haemodynamic alterations. (c) All HRV measures showed an increase in the parasympathetic activity. (d) If a physiological HRV is a mechanism for providing adaptability and flexibility, diving should not provoke circulatory problems in healthy subjects. (e) Either a lower than normal HRV under control conditions or a reduction in HRV induced by diving would be unphysiological, and a scuba diving candidate showing such characteristics should be further investigated.

Adult↗
PubMed1999

Open water scuba diving accidents at Leicester: five years' experience.

OBJECTIVES: The aim of this study was to determine the incidence, type, outcome, and possible risk factors of diving accidents in each year of a five year period presenting from one dive centre to a large teaching hospital accident and emergency (A&E) department. METHODS: All patients included in this study presented to the A&E department at a local teaching hospital in close proximity to the largest inland diving centre in the UK. Our main outcome measures were: presenting symptoms, administration of recompression treatment, mortality, and postmortem examination report where applicable. RESULTS: Overall, 25 patients experienced a serious open water diving accident at the centre between 1992 and 1996 inclusive. The percentage of survivors (n = 18) with symptoms of decompression sickness receiving recompression treatment was 52%. All surviving patients received medical treatment for at least 24 hours before discharge. The median depth of diving accidents was 24 metres (m) (range 7-36 m). During the study period, 1992-96, the number of accidents increased from one to 10 and the incidence of diving accidents increased from four per 100,000 to 15.4 per 100,000. Over the same time period the number of deaths increased threefold. CONCLUSIONS: The aetiology of the increase in the incidence of accidents is multifactorial. Important risk factors were thought to be: rapid ascent (in 48% of patients), cold water, poor visibility, the number of dives per diver, and the experience of the diver. It is concluded that there needs to be an increased awareness of the management of diving injuries in an A&E department in close proximity to an inland diving centre.

Accidents↗
PubMed1987

Heart rate and body temperature during free diving of Weddell seals.

We have developed and successfully used the first microprocessor-controlled monitors for collection of data on depth, heart rate, and body temperature of one fetal and five adult male freely swimming Weddell seals. Adult seals almost invariably experienced a prompt bradycardia at the start of each dive, and the mean heart rate during diving was significantly lower for dives greater than 20 min (P greater than 0.999). The heart rate was also significantly greater during the ascent portion of dives when compared with the descent portion (P greater than 0.95). The fetal seal experienced a slow onset of bradycardia when its mother dived; during diving the fetal heart rate decreased by an average of 1.1 beats/min for each minute of the dive. The fetal heart rate generally took approximately 10 min to recover to predive levels after its mother resurfaced to breathe. The body temperature of one adult male Weddell seal showed a decrease of greater than 1.5 degrees C from resting levels before dives of greater than 15 min were initiated and a drop of over 2 degrees C before dives of greater than 30 min duration.

Animals↗
PubMed1980

Fetal cardiovascular and metabolic responses to simulated diving in the Weddell seal.

Fetal responses to normobaric diving simulated by submersion of the maternal head for 20 min were studied in four conscious Weddell seals near term. Microspheres injected into the maternal aorta were distributed to the placenta and kidneys in the ratio of 0.4 in the control period and 19.3 during diving, suggesting minimal placental vasoconstriction. Fetal heart rate fell during diving from a mean control value of 90 to 34 beats/min after 4 min. The onset of fetal bradycardia was not consistently associated with changes in blood gas tensions. Diving was associated with a fall in fetal arterial O2 tension from 24 to 9 Torr, arterial CO2 tension rose from 47 to 85 Torr, and arterial pH fell from 7.35 to 7.24. Fetal-maternal gradients for CO2 and H+ transport remained constant, whereas the gradient for O2 transport fell from 47 Torr before diving to 14 Torr at the end of diving. Blood lactate concentrations increased three- to fourfold during diving and reached peak values 10-15 min after diving ended. The similarity of the fetal and maternal heart rate responses to diving is consistent with the presence of physiological oxygen-conserving reflexes akin to the adult's.

Animals↗
PubMed2002

The human spleen as an erythrocyte reservoir in diving-related interventions.

Twelve subjects without and ten subjects with diving experience performed short diving-related interventions. After labeling of erythrocytes, scintigraphic measurements were continuously performed during these interventions. All interventions elicited a graduated and reproducible splenic contraction, depending on the type, severity, and duration of the interventions. The splenic contraction varied between approximately 10% for "apnea" (breath holding for 30 s) and "cold clothes" (cold and wet clothes applied on the face with no breath holding for 30 s) and approximately 30-40% for "simulated diving" (simulated breath-hold diving for 30 s), "maximal apnea" (breath holding for maximal duration), and "maximal simulated diving" (simulated breath-hold diving for maximal duration). The strongest interventions (simulated diving, maximal apnea, and maximal simulated diving) elicited modest but significant increases in hemoglobin concentration (0.1-0.3 mmol/l) and hematocrit (0.3-1%). By an indirect method, the splenic venous hematocrit was calculated to 79%. No major differences were observed between the two groups. The splenic contraction should, therefore, be included in the diving response on equal terms with bradycardia, decreased peripheral blood flow, and increased blood pressure.

Adult↗
PubMed1997

Physiology of diving of birds and mammals.

This review concentrates on the physiological responses, and their control, in freely diving birds and mammals that enable them to remain submerged and sometimes quite active for extended periods of time. Recent developments in technology have provided much detailed information on the behavior of these fascinating animals. Unfortunately, the advances in technology have been insufficient to enable physiologists to obtain anything like the same level of detail on the metabolic rate and physiological adjustments that occur during natural diving. This has led to much speculation and calculations based on many assumptions concerning usable oxygen stores and metabolic rate during diving, in an attempt to explain the observed behavior. Despite their shortcomings, these calculations have provided useful insights into the degree of adaptations of various species of aquatic birds and mammals. Many of them, e.g., ducks, smaller penguins, fur seals, and Weddell seals, seem able to metabolize aerobically, when diving, at approximately the same (if not greater) rate as they do at the surface. Their enhanced oxygen stores are able to support aerobic metabolism, at what would not be considered unusually low levels, for the duration of the dives, although there are probably circulatory readjustments to ensure that the oxygen stores are managed judiciously. For other species, such as the larger penguins, South Georgian shag, and female elephant seals, there is a general consensus that they must either be reducing their aerobic metabolic rate when diving, possibly by way of regional hypothermia, and/or producing ATP, at least partly, by anaerobiosis and metabolizing the lactic acid when at the surface (although this is hardly likely in the case of the female elephant seals). Circulation is the proximate regulator of metabolism during aerobic diving, and heart rate is the best single indicator of circulatory adjustment. During voluntary dives, heart rates range from extreme bradycardia to well above resting, reflecting metabolic performance. Efferent cardiac control is largely parasympathetic. Reflex cardiorespiratory responses are modulated by conditioning and habituation, but reflexes predominate during extended dives and during recovery, when gas exchange is maximized.

Adenosine Triphosphate↗
PubMed2005

Do seasonal changes in metabolic rate facilitate changes in diving behaviour?

Macaroni penguins were implanted with data loggers to record heart rate (fH), abdominal temperature (Tab) and diving depth during their pre-moult trip (summer) and winter migration. The penguins showed substantial differences in diving behaviour between the seasons. During winter, mean and maximum dive duration and dive depth were significantly greater than during summer, but the proportion of dives within the calculated aerobic dive limit (cADL) did not change. Rates of oxygen consumption were estimated from fH. As winter progressed, the rate of oxygen consumption during dive cycles (sVO2DC)) declined significantly and mirrored the pattern of increase in maximum duration and depth. The decline in sVO2DC) was matched by a decline in minimum rate of oxygen consumption (sVO2min)). When sVO2min) was subtracted from sVO2DC), the net cost of diving was unchanged between summer and winter. We suggest that the increased diving capacity demonstrated during the winter was facilitated by the decrease in sVO2min). Abdominal temperature declined during winter but this was not sufficient to explain the decline in sVO2min). A simple model of the interactions between sVO2min), thermal conductance and water temperature shows how a change in the distribution of fat stores and therefore a change in insulation and/or a difference in foraging location during winter could account for the observed reduction in sVO2min) and hence sVO2DC).

Animals↗