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At least 253 records · Page 14Linked to original sources
PubMed2003

Arterial blood gases during diving in elite apnea divers.

Elite apnea divers have considerably extended the limits of dive depth and duration but the mechanisms allowing humans to tolerate the compression- and decompression-induced changes in alveolar gas partial pressures are still not fully understood. Therefore we measured arterial blood gas tensions and acid-base-status in two elite apnea divers during simulated wet dives lasting 3 : 55 and 5 : 05 minutes, respectively. Arterial pO2 followed the compression-(from 13.8/16.9 kPa before the dive to 30 kPa at the start of the bottom time) and decompression-induced (from 13.7/21.0 kPa to 3.3/4.9 kPa immediately after surfacing) variations of ambient pressure, while the arterial pCO2 remained within the physiologic range (3.0/3.9 kPa before diving vs. 5.7/5.9 kPa at the end of the bottom time), probably due to the CO2 storage capacity of the blood. These findings may help to explain why humans can sustain deep and long apnea dives without major increases in respiratory drive.

Acid-Base Equilibrium↗
PubMed1997

Diving and swimming performance of white whales, Delphinapterus leucas: an assessment of plasma lactate and blood gas levels and respiratory rates.

The white whale Delphinapterus leucas is an exceptional diver, yet we know little about the physiology that enables this species to make prolonged dives. We studied trained white whales with the specific goal of assessing their diving and swimming performance. Two adult whales performed dives to a test platform suspended at depths of 5-300 m. Behavior was monitored for 457 dives with durations of 2.2-13.3 min. Descent rates were generally less than 2 m s-1 and ascent rates averaged 2.2-3 m s-1. Post-dive plasma lactate concentration increased to as much as 3.4 mmol l-1 (4-5 times the resting level) after dives of 11 min. Mixed venous PO2 measured during voluntary breath-holds decreased from 79 to 20 mmHg within 10 min; however, maximum breath-hold duration was 17 min. Swimming performance was examined by training the whales to follow a boat at speeds of 1.4-4.2 m s-1. Respiratory rates ranged from 1.6 breaths min-1 at rest to 5.5 breaths min-1 during exercise and decreased with increasing swim speed. Post-exercise plasma lactate level increased to 1.8 mmol l-1 (2-3 times the resting level) following 10 min exercise sessions at swimming speeds of 2.5-2.8 m s-1. The results of this study are consistent with the calculated aerobic dive limit (O2 store/metabolic rate) of 9-10 min. In addition, white whales are not well adapted for high-speed swimming compared with other small cetaceans.

Animals↗
PubMed2002

Stroke in a scuba diver with patent foramen ovale.

Patent foramen ovale (PFO) is a frequent condition which carries a significant risk for stroke when associated with deep venous thrombosis and primary or secondary coagulation abnormalities. Here, we describe a patient in which scuba diving is thought to be associated with stroke in a subject with an otherwise clinically silent PFO. During a rapid ascent a 43-year-old-scuba diver reported weakness and paresthesias in the right arm which lasted about 10 min. He presented similar symptoms 2 days later 1 h after diving, and a third time on his flight back home. The MRI showed multiple hyperintense areas on T2-weighted images in the white matter. Transoesophageal echocardiography (TEE) showed a PFO, whilst all haematological and haemocoagulation tests were negative. Scuba diving may constitute a patho-physiological condition in the presence of PFO as breath-holding promotes right-to-left shunt and arterialization of venous bubbles.

Adult↗
PubMed1994

Gas exchange of captive freely diving grey seals (Halichoerus grypus).

When at sea, phocids dive for long periods and spend a high percentage of their time submerged. This behaviour requires some combination of an increased oxygen storage capacity, rapid oxygen loading at the surface and reduced oxygen utilisation when submerged. To assess these adaptations, breath-by-breath ventilation was studied in four adult grey seals (two male, two female, 160-250 kg), freely diving in a large outdoor tank where surface access was restricted to one breathing hole. The dive patterns obtained were similar to those recorded from freely diving wild grey seals. Respiratory frequency during the surface periods was 40% higher than that estimated from allometric relationships (19.4 +/- 0.7 breaths min-1), and tidal volume (6.3 +/- 1.21) was approximately five times higher than that estimated from allometric relationships. These adaptations produce a high minute volume and enable gas exchange to occur at the surface. Mean oxygen consumption rate (VO2, measured for a dive+surface cycle) decreased with increasing dive duration. The aerobic dive limit was estimated as 9.6 min for a 150 kg grey seal (using the overall average VO2 of 5.2 ml O2 min-1 kg-1), which is consistent with results from freely diving wild grey seals (only 6% of dives exceeded 10 min). End-tidal oxygen values varied during a surface period, following a U-shaped curve, which suggests that there is limited oxygen uptake from the lung and/or blood oxygen stores during dives. This result was unexpected and indicates that these seals are utilising substantial physiological responses to conserve oxygen, even during shallow voluntary diving.

Animals↗
PubMedDate not supplied

Psychophysiologic changes in sleep during simulated 200-m heliox saturation dives.

The standard polysomnogram and questionnaire were measured from 4 subjects during 2 simulated 200-m heliox saturation dives. These measurements were performed for 1 precompression night, bottom nights, 4 or 5 nights during decompression, and 1 postdecompression night. Although the subjects reported a marked decrease in quantity and quality of sleep at the bottom, only a slight degree of sleep disturbance caused by frequent awakenings was found in polysomnograms. Throughout the dive period, latency of each sleep stage, quantity of REM sleep, and the REM-NREM cycle showed no changes, whereas quantity of slow wave sleep remained at a low level. From these results it was inferred that basic sleep mechanisms were not affected under 200-m heliox environment. Unusual physiologic phenomena were observed during the dive period. Intermittent diffuse rhythmic theta activity was found in 1 subject at sleep stage REM during the bottom. Rhythmic contraction of facial muscles, which was similar to bruxism, increased, particularly at sleep stage 2 in all subjects during decompression.

Adult↗
PubMed1997

Use of neural networks in telemedical monitoring of divers.

An artificial neural network (ANN) has been developed to predict and classify the risk of medical disorders for certain dive profiles. The telemedical data applied to the ANN represent different physiological and physical parameters that are transmitted acoustically from a diver to a remote receiver. The telemetered data include dive time, maximum depth and decompression stop times and depths. Preliminary tests demonstrated the successful performance of the ANN where classical mathematical and statistical methods had failed due to the complex nature and variability of the parameters involved.

Diving↗
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↗
PubMed1987

Respiratory effects of a single saturation dive to 300 m.

Lung function and the response to exercise were monitored in seven diver/welders who took part in a test saturation dive to 300 m for an average duration of 12 days; decompression took an average of nine days. Immediately after the dive the forced vital capacity was increased above base line by on average 0.51, the forced expiratory volume by 0.281 and peak expiratory flow rate by 0.71 s-1. There was no change in flow rate at small lung volumes (FEF 75% FVC). Recovery was complete and appeared to have a half time of 28 days. Transfer factor of the lungs for carbon monoxide (TlCO) was reduced by on average 9.6% after the dive but while partial recovery occurred, the values at one year were on average lower than those observed initially. The reason is unclear. One subject developed transient oxygen toxicity with stiff lungs and increased ventilation and cardiac frequency during submaximal exercise; a second subject developed similar changes but without accompanying symptoms. There is need for detailed physiological surveillance of people undertaking deep dives; this should be undertaken in circumstances that permit accurate measurements and full subject cooperation.

Adult↗
PubMed2005

Peter Hochachka: adventures in biochemical adaptation.

Peter Hochachka was one of the most creative forces in the field of comparative physiology during the past half-century. His career was truly an exploratory adventure, in both intellectual and geographic senses. His broad comparative studies of metabolism in organisms as diverse as trout, tunas, oysters, squid, turtles, locusts, hummingbirds, seals, and humans revealed the adaptable features of enzymes and metabolic pathways that provide the biochemical bases for diverse lifestyles and environments. In its combined breadth and depth, no other corpus of work better illustrates the principle of "unity in diversity" that marks comparative physiology. Through his publications, his stimulating mentorship, his broad editorial services, and his continuous-and highly infectious-enthusiasm for his field, Peter Hochachka served as one of the most influential leaders in the transformation of comparative physiology.

Adaptation, Physiological↗
PubMed1981

Relative contributions of chemical and non-chemical drives to the breath-holding time in breath-hold divers (Ama).

Relative contributions of chemical and non-chemical respiratory stimulations to breath-holding time (BHT) were examined in assisted (Funado) and unassisted (Kachido) breath-hold divers (Ama). In the Funado the magnitude of the chemical contribution was reduced, though statistically not significantly. On the other hand, in the Kachido no difference in chemical contribution was seen from the control. This was considered to be due to the fact that ventilatory response to CO2 was reduced in the Funado, but not in the Kachido. Despite the decreased contribution of CO2 drive to BHT, absolute BHT in the Funado was no prolonged. This may be related to sensitization of the respiratory centers to non-chemical stimulation. Such adaptation would be effective for preventing the danger of losing consciousness in the Funado who face extreme hypoxia on returning to the surface from a dive.

Adaptation, Physiological↗