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Biomedical subjects

C E Lundgren

Publications and source records attributed to C E Lundgren.

At least 37 records · Page 2Linked to original sources
PubMed1988

Prostacyclin does not change during an oxygen induced increase in pulmonary blood flow in the fetal lamb.

The role of prostacyclin in mediating the increase in pulmonary blood flow caused by an increase in oxygen tension in the fetal lamb was investigated. Plasma concentrations of 6-keto-PGF1 alpha, the hydrolysis product of prostacyclin, were measured during an increase in pulmonary blood flow caused by a rise in oxygen tension in eight intrauterine fetal lambs. Fetal oxygen tension was increased by placing the pregnant ewes in a hyperbaric chamber and having them breathe 100% oxygen at three atmospheres absolute pressure. This increased fetal PaO2 from 27 +/- 3 to 60 +/- 6 torr (mean +/- S.E., p less than or equal to 0.0001) and increased the proportion of right ventricular output distributed to the fetal lungs from 6 +/- 2 to 45 +/- 7% (mean +/- S.E., p less than or equal to 0.001). However, the fetal plasma concentration of 6-keto-PGF1 alpha did not change, 186 +/- 26 to 208 +/- 40 pg/ml (mean +/- S.E.). Indomethacin decreased plasma concentrations of 6-keto-PGF1 alpha in each of three fetuses but did not decrease the proportion of right ventricular output distributed to their lungs. The increase in pulmonary blood flow caused by an increase in oxygen tension in the fetal lamb is not associated with an increase in plasma concentrations of 6-keto-PGF1 alpha. Prostacyclin does not appear to be involved in the increase in pulmonary blood flow caused by the increase in oxygen tension at birth.

Animals↗
PubMed1988

Breath-hold duration in man and the diving response induced by face immersion.

The objective of this study in 5 selected volunteer subjects was to see whether the circulatory diving response which is elicited by breath holding and by cold water on the face would affect the duration of maximal-effort breath holds. Compared to control measurements (breath holding during resting, breathing with 35 degrees C water on the face) breath holding with the face cooled by 20 degrees C water caused a 12% reduction of heart rate, 6% reduction of cardiac output, 33% reduction in [corrected] forearm blood flow, and 9% rise in mean arterial blood pressure, but there was no difference in breath-hold duration (control and experimental both 94 s). There were also no differences in time of appearance of the first involuntary respiratory efforts during breath holding, in alveolar gas exchange, or in breaking-point alveolar O2 and CO2 tensions. When the diving response was magnified by a brief bout of exercise so that there was a 19% [corrected] reduction in heart rate, 23% reduction in cardiac output, and 48% reduction in forearm blood flow, breath-hold duration was still unaffected by face cooling. Compared to intermittent immersions, continuous exposure of the face to cold water abolished the diving response, probably by a cold adaptation of facial thermal receptors. These results with cooling of the face only are consistent with our earlier finding that there was a negative correlation between the duration of a maximal-effort breath hold and the diving response during whole-body submersion in cold water.

Adult↗
PubMed1987

Simulated breath-hold diving to 20 meters: cardiac performance in humans.

Cardiac performance was assessed in six subjects breath-hold diving to 20 m in a hyperbaric chamber, while nonsubmersed or submersed in a thermoneutral environment. Cardiac index and systolic time intervals were obtained with impedance cardiography and intrathoracic pressure with an esophageal balloon. Breath holding at large lung volume (80% vital capacity) decreased cardiac index, probably by increasing intrathoracic pressure and thereby impeding venous return. During diving, cardiac index increased (compared with breath holding at the surface) by 35.1% in the nonsubmersed and by 29.5% in the submersed condition. This increase was attributed to a fall in intrathoracic pressure. Combination of the opposite effects of breath holding and diving to 20 m left cardiac performance unchanged during the dives (relative to the surface control). A larger intrathoracic blood redistribution probably explains a smaller reduction in intrathoracic pressure observed during submersed compared with nonsubmersed diving. Submersed breath-hold diving may entail a smaller risk of thoracic squeeze (lesser intrathoracic pressure drop) but a greater risk of overloading the central circulation (larger intrathoracic blood pooling) than simulated nonsubmersed diving.

Adult↗
PubMed1987

A comparison of respiratory function in divers breathing with a mouthpiece or a full face mask.

A comparison was made of respiratory function in submersed divers breathing with either a mouthpiece or a full face mask while exposed to varying depths (15 and 190 fsw), exercise loads (0-175 W), and static lung loads (0 and -20 cmH2O). The two types of breathing equipment were designed to be identical in terms of functional dead space volume and resistance to gas flow. When compared with data from experiments utilizing a full face mask, use of a mouthpiece caused a modest fall in expired minute volume at both depths. The majority of this decline may have been the consequence of a decrease in dead space ventilation brought about by the elimination of simultaneous nose breathing and mouth breathing. Alveolar ventilation and PETCO2 were not significantly influenced by the use of a mouthpiece, regardless of depth, workload, or static lung load. With both types of breathing gear episodes of dyspnea were infrequent during experiments with a static lung load of 0 cmH2O. Therefore, if a neutral static lung load is maintained, the type of breathing gear used does not seem to be of consequence as far as dyspnea is concerned.

Adult↗
PubMed1987

Respiratory function in the upright, working diver at 6.8 ATA (190 fsw).

The influence of static lung loading on a number of respiratory parameters was investigated in subjects performing graded leg exercise in an upright posture while submerged and breathing air at ambient pressures up to 6.76 ATA. In comparison with a previous investigation of the prone posture, a lesser tendency to dyspnea was observed. Neutral and moderately positive static lung loads were associated with less dyspnea than were negative loads. Several indices of respiratory function remained relatively normal during exercise and exposure to varying static lung loads. However, there was a tendency for hypoventilation and CO2 accumulation during heavy exercise at 190 fsw; this was not strictly correlated with dyspnea or static lung load. We conclude that, if a full face mask is used, breathing gear for divers should provide a static lung load of approximately 0 to +10 cmH2O regardless of the diver's orientation in the water. When possible, divers should assume an upright posture while engaged in strenuous work.

Analysis of Variance↗
PubMed1986

Cardiac performance in humans during breath holding.

The effects on cardiac performance of high and low intrathoracic pressures induced by breath holding at large and small lung volumes have been investigated. Cardiac index and systolic time intervals were recorded from six resting subjects with impedance cardiography in both the nonimmersed and immersed condition. A thermoneutral environment (air 28 degrees C, water 35 degrees C) was used to eliminate the cold-induced circulatory component of the diving response. Cardiac performance was enhanced during immersion compared with nonimmersion, whereas it was depressed by breath holding at large lung volume. The depressed performance was apparent from the decrease in cardiac index (24.1% in the immersed and 20.9% in the nonimmersed condition) and from changes in systolic time intervals, e.g., shortening of left ventricular ejection time coupled with lengthening of preejection period. In the absence of the cold water component of the diving response, breath holding at the large lung volume used by breath-hold divers tends to reduce cardiac performance presumably by impeding venous return.

Adult↗
PubMed1985

Diving bradycardia and breath-holding time in man.

The hypothesis that the diving response, recorded as diving bradycardia during submersed breath holding in man, would enhance his breath-holding time was tested. Five certified scuba divers served as subjects. They performed breath holds of maximal duration while nonimmersed and during submersion in cool (32 degrees C), cold (20 degrees C), and thermoneutral (35 degrees C) water. The mean breath-holding time and heart rate during the nonimmersed (control) condition were, respectively, 111.2 +/- 14.1 (SE) s and 64.1 +/- 4.7 (SE) beats/min, the relatively long breath-holding times being due primarily to the so-called short-term training effect. Compared to the control values the breath-holding time in 20 degrees C water was 54.9% shorter and heart rate 25.9% lower, in 32 degrees C water the breath-holding time was not different and heart rate was 28.1% lower, and in 35 degrees C water the breath-holding time was longer by 25.6% while there was no difference in heart rate. In all conditions the breath-hold breaking point alveolar PCO2 was the same at about 52 mmHg. The shortening of the breath holds in cold water was ascribed to a 256% increase (over nonimmersed control) in metabolic rate as well as a respiratory drive due to stimulation of skin cold receptors. As for the prolongation of breath holds in thermoneutral water, it was hypothesized that immersion caused a delay in the build-up of chemical stimuli at the chemoreceptors.

Adult↗
PubMed1984

Respiratory function during simulated wet dives.

This presentation focuses on the effects of static lung loading (SLL) on diver performance. It is noted that SLL may arise from depth differences between the diver's chest and his breathing gear. Studies are reviewed in which subjects undergoing wet, simulated dives in a pressure chamber were exposed to SLL ranging from 14.7 to -14.7 mmHg (+20 to -20 cmH2O) while breathing air at depths down to 58 m (190 ft). The subjects, assuming a prone or an upright position, performed leg exercise on an underwater bicycle ergometer. Various measurements of respiratory function were made. By applying a scoring scale for dyspnea it was found that in addition to being more pronounced as exercise and depth (gas density) increased, the dyspnea was most pronounced with negative SLL. Positive SLL alleviated the dyspnea. The dyspnea also tended to be more pronounced in the prone than in the upright posture. It was speculated that this may have been partly due to more of a compression effect on the extra thoracic airways by water pressure in the former than in the latter posture. There were no marked differences in gas exchange and end-tidal gas concentrations with different static lung loads, and it was hypothesized that differences in respiratory muscular strain may have accounted for the differences in dyspnea with different SLLs. That the dyspnea was inspiratory in nature would agree with the observation that positive SLL aiding inspiration would be perceived as beneficial. A breathing apparatus design that counteracts undesirable SLL is reviewed.

Biomechanical Phenomena↗
PubMed1983

Influence of exercise on maximal voluntary ventilation and forced expiratory flow at depth.

Four to six subjects performed maximal voluntary ventilation (MVV) and forced expirations during rest, exercise (50, 125, and 200 W), and inhalation of air and CO2 and air at rest while submerged at pressures of 1.45, 2.82, 4.64, and 6.76 atm. Maximal expiratory flow (at 40% of vital capacity) and MVV at rest decreased as exponential functions of gas density, but the decrease was less than in some earlier studies. Independent of pressure, MVV increased by about 10%-17% at the heavier work loads and expiratory flow increased by 27%-48%; the increase in expiratory flow disappeared within 2 min after exercise. Exercise increased end-tidal CO2 tension by up to 9 mmHg. Carbon dioxide inhalation increasing the end-tidal level by up to about 25 mmHg during rest had no effect on MVV and a slight to moderate effect on flow, increasing it by a maximum of 21% at 4.64 atm. The enhancing effect of exercise on MVV and expiratory flow at depth apparently was mainly due to modified autonomic nervous activity reducing pulmonary flow resistance, CO2 accumulation playing an uncertain role, and passive distension of airways playing no role.

Adult↗
PubMed1979

Effects of immersion and static lung loading on submerged exercise at depth.

The effects of static lung loading in the range +20 cmH2O to -20 cmH2O was investigated in 3 male subjects breathing air during submerged exercise in the prone position at pressures ranging from 1.45 ATA to 6.76 ATA. Both maximal and submaximal exercise was performed and dry controls were done at 1.45 ATA. A low-resistance bag-in-a-box breathing apparatus (less than 1.25 cmH2O/liter/s at 8 g/liter density) was used. Static lung loading had little effect on maximal or submaximal VO2, VCO2, VE, heart rate, or end-tidal PCO2, while increased breathing gas density did affect these parameters to a larger extent. Imersion per se reduced the VE at a given level of VO2 and increased both the VT and VA at a given VE. Increasingly positive static lung load increased VC and ERV both during rest and exercise. Exercise-induced dyspnea was experienced and scored. At submaximal VO2 levels up to 2.5 liter/min this dyspnea did not limit exercise at any depth, but during maximal exertion at 6.76 ATA (VO2 from 3.45--3.77 liter/min), dyspnea became work limiting in several cases. Static load had a marked effect on dyspnea and a load of +10 cmH2O produced the least dyspnea, enabling all subjects to perform maximal exertions for 5 min at 6.76 ATA. The 15-s MVV was performed at all depths and static loads and neither it nor the VE/MVV ratio correlated with the degree of dyspnea.

Adult↗
PubMed1978

Chamber-based system for physiological monitoring of submerged exercising subjects.

A system has been designed which allows for measurement of cardiorespiratory parameters in the fully submerged subject performing graded exercise. It consists of a horizontal wet chamber; a waterproofed, electrically braked bicycle ergometer; and a low-resistance "bag-in-a-box" breathing apparatus. Chamber and breathing apparatus design allow for a great deal of flexibility in both positioning of the subject and instrumentation. The 200-liter "bag-in-a-box" configuration provides the subject with humidified gas through 2.5 in. i.d. tubing. A rolling seal spirometer provides the lung counter volume. Provision is made for breath-by-breath gas analysis with a mass spectrometer. Hydrostatic pressure on the diver's thorax relative to chamber pressure can be easily and reproducibly varied over a wide range of positive and negative static lung loads. This system has been used on over 100 man-dives to depths equivalent to 6.5 ATA with oxygen consumptions up to 4.0 liters/min.

Humans↗
PubMed1977

Eustachian tubal function during immersion.

The effects of head-out immersion on active and passive middle ear pressure equilibration were studied in three otologically normal scuba divers. Results were compared with the equilibration capacity recorded in the nonimmersed sitting and supine positions. Head-out immersion had only a minor effect on the ability to equilibrate the middle ear pressure actively during descent; passive ear clearing during ascent was slightly more difficult compared with this capacity in the sitting nonimmersed position. In the supine position ear clearing was significantly more difficult during both ascent and descent, which indicates that it is preferable to assume an upright body posture during exposures to pressure changes in dry pressure chambers. Mechanisms that might influence the ability to equilibrate the middle ears are discussed.

Adult↗
PubMed1976

Heart rate and respiratory frequency in hydrostatically compressed, liquid-breathing mice.

The effects of hydraulic compression on heart rate and respiratory frequency were studied in liquid-breathing, hypothermic (17-31 degrees C) mice. Increasing the hydrostatic pressure caused a bradycardia that was first evident at 25 at. and progressed to 48% of the control heart rate at 175 at. The bradycardia was reversed, although incompletely, by decompression. Similar changes in respiratory frequency were seen. Autonomic blockage with atropine and propranolol did not change the response patterns to any major extent. Compression rate (2-6 at. x min-1) did not seem to influence the degree of heart-rate reduction. Compression caused an increase in colonic temperature, and decompression a decrease (0.5 degree C for a pressure change of 100 at.). These temperature changes could be ascribed partly to adiabatic heating and cooling of the body tissues as revealed by similar changes in dead animals and partly to increased metabolic heat generation in connection with compression-induced convulsions. The temperature changes, although partly accounting for the hysteresis in the heart-rate changes during compression/decompression, were not responsible for the major effects. It was concluded that high pressure causes bradycardia by a direct action on cardiac-pacemaker cells.

Animals↗
PubMed1975

Nausea and abdominal discomfort--possible relation to aerophagia during diving: an epidemiologic study.

Gastrointestinal (GI) distension by gas expansion may be more of a problem in diving than is usually recognized. In response to a written questionnaire, 2053 scuba divers gave information about GI discomfort such as pain, nausea, and vomiting in connection with diving. One hundred and eleven reports (5.4% of 2053) were considered possible cases of significant GI distension because the majority of divers had their symptoms during ascent and a significant number of them got relief from belching. Difficult middle ear pressure equilibration was a particular problem among divers with GI symptoms. It may have induced frequent swallowing, causing air ingestion and consequent GI problems. Steep, head-first descents appear to have been employed in some dives, leading to GI discomfort presumably be creating large mouth-to-stomach gas-pressure differences. It was concluded that swallowing or any procedure leading to entry of gas into the stomach should be avoided and that belching during diving should be recommended.

Abdominal Pain↗
PubMed1975

Influence of body posture and ear clearing on body buoyancy during diving.

The amount of gas introduced into the gastrointestinal (GI) tract during diving was studied by underwater weighing. The influence of body posture and ear clearing methods was determined. Ten subjects were studied in wet simulated dives to a 30-m depth. Clearing the ears by swallowing and descending head first gave a mean weight reduction (before dive-after dive) of 0.29 kg; descending in the upright position gave a mean weight reduction of 0.16 kg. Swallowing during descent (upright posture) caused a 0.11 kg greater weight reduction than blowing against the clamped nose. The greatest weight reduction (1.34 kg) occurred in a head-first dive (swallowing) with 7 cycles of depth changes between 30 and 25 m. During the ascent the subject experienced considerable abdominal discomfort. It was concluded that swallowing during diving, particularly in the head-down position, may introduce large amounts of gas into the GI tract and that during diving one should try to eliminate ingested gas by belching.

Aerophagy↗