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At least 127 records · Page 7Linked to original sources

PubMed1986

Passive mechanics of upright human chest wall during immersion from hips to neck.

We have determined the mechanical effects of immersion to the neck on the passive chest wall of seated upright humans. Repeated measurements were made at relaxed end expiration on four subjects. Changes in relaxed chest wall configuration were measured using magnetometers. Gastric and esophageal pressures were measured with balloon-tipped catheters in three subjects; from these, transdiaphragmatic pressure was calculated. Transabdominal pressure was estimated using a fluid-filled, open-tipped catheter referenced to the abdomen's exterior vertical surface. We found that immersion progressively reduced mean transabdominal pressure to near zero and that the relaxed abdominal wall was moved inward 3-4 cm. The viscera were displaced upward into the thorax, gastric pressure increased by 20 cmH2O, and transdiaphragmatic pressure decreased by 10-15 cmH2O. This lengthened the diaphragm, elevating the diaphragmatic dome 3-4 cm. Esophageal pressure became progressively more positive throughout immersion, increasing by 8 cmH2O. The relaxed rib cage was elevated and expanded by raising water from hips to lower sternum; this passively shortened the inspiratory intercostals and the accessory muscles of inspiration. Deeper immersion distorted the thorax markedly: the upper rib cage was forced inward while lower rib cage shape was not systematically altered and the rib cage remained elevated. Such distortion may have passively lengthened or shortened the inspiratory muscles of the rib cage, depending on their location. We conclude that the nonuniform forcing produced by immersion provides unique insights into the mechanical characteristics of the abdomen and rib cage, that immersion-induced length changes differ among the inspiratory muscles according to their locations and the depth of immersion, and that such length changes may have implications for patients with inspiratory muscle deficits.

Abdomen↗

PubMed1989

Lithium clearance in water immersion-induced natriuresis in humans.

Lithium clearance (CLi) has been advanced as a measure of sodium delivery from the proximal tubules. Because information on the intrarenal effects of water immersion is only limited, and available data are conflicting with respect to the effects on the proximal tubule, we examined the effects of 3 h of water immersion on renal functional parameters, including CLi, in eight healthy subjects. Studies were carried out during maximal water diuresis. Water immersion resulted in a significant increase in sodium excretion, from preimmersion values of 74.0 +/- 9.6 to 155.4 +/- 12.0 mumol/min at the third immersion hour (P less than 0.01). This natriuresis was accompanied by an increase in CLi from 26.3 +/- 1.9 (preimmersion) to 37.0 +/- 3.1 ml/min (P less than 0.01). Fractional lithium reabsorption (FRLi) decreased from 76.4 +/- 1.0 to 69.6 +/- 1.3% (P less than 0.01). None of these changes was found in eight healthy subjects undergoing a time-control study without water immersion. The large fall in FRLi found during immersion is compatible with a major resetting of the proximal glomerulotubular balance. In this regard the renal response to water immersion resembles saline expansion rather than mere intravascular expansion. The lithium data suggested a large rise in distal delivery accompanied by an almost as large rise in distal reabsorption. The free water clearance data were in agreement with this interpretation. However, no changes were found in fractional excretion of phosphate and uric acid. Therefore such a major resetting of proximal glomerulotubular balance can be doubted.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1999

Static respiratory muscle work during immersion with positive and negative respiratory loading.

Upright immersion imposes a pressure imbalance across the thorax. This study examined the effects of air-delivery pressure on inspiratory muscle work during upright immersion. Eight subjects performed respiratory pressure-volume relaxation maneuvers while seated in air (control) and during immersion. Hydrostatic, respiratory elastic (lung and chest wall), and resultant static respiratory muscle work components were computed. During immersion, the effects of four air-delivery pressures were evaluated: mouth pressure (uncompensated); the pressure at the lung centroid (PL,c); and at PL,c +/-0.98 kPa. When breathing at pressures less than the PL,c, subjects generally defended an expiratory reserve volume (ERV) greater than the immersed relaxation volume, minus residual volume, resulting in additional inspiratory muscle work. The resultant static inspiratory muscle work, computed over a 1-liter tidal volume above the ERV, increased from 0.23 J. l(-1), when subjects were breathing at PL,c, to 0.83 J. l(-1) at PL,c -0.98 kPa (P < 0.05), and to 1.79 J. l(-1) at mouth pressure (P < 0.05). Under the control state, and during the above experimental conditions, static expiratory work was minimal. When breathing at PL,c +0.98 kPa, subjects adopted an ERV less than the immersed relaxation volume, minus residual volume, resulting in 0.36 J. l(-1) of expiratory muscle work. Thus static inspiratory muscle work varied with respiratory loading, whereas PL,c air supply minimized this work during upright immersion, restoring lung-tissue, chest-wall, and static muscle work to levels obtained in the control state.

Adult↗

PubMed1982

Renal phosphate handling in nephrotic syndrome during water immersion.

In 11 patients suffering from nephrotic syndrome, renal phosphate handling was studied in water immersion up to the neck. There was a rapid onset of phosphate diuresis which continued to increase throughout water immersion; and an increase in fractional excretion of phosphate (FEPO4) continuing throughout immersion and decreasing in the hour after immersion. TmPO4/GFR did not change on immersion. TmPO4/Inulin clearance gave higher figures than TmPO4/creatinine clearance due to secretion of creatinine in 9 of 11 patients. There was a transitory increase in PTH during immersion, but mean immersion plasma levels of PTH did not change when compared to preimmersion control values. FEPO4 was more frequently significantly correlated with FECL than to FENa in nephrotics.

Chlorides↗

PubMed1995

Influence of cold water immersion on heat debt and substrate utilization in males varying in body composition: a retrospective analysis.

The present article is a retrospective analysis of previously published data. This analysis examined the effect of immersion in 18, 22 and 26 degrees C cold water, on heat debt (kJ), substrate utilization [i.e., R (respiratory exchange ratio) calculated using indirect calorimetry], and aerobic metabolic rate (i.e., VO2 (oxygen consumption) 1 # min(-1)] in 24 male volunteers (20-35 years) given a preexposure meal (60.2 g carbohydrate, 12.0 g protein, and 2.8 g fat at 60 min prior to the experimental trial) and examined during 90 min of immersion to the first thoracic vertebrae. Body composition was determined via underwater densitometry. Subjects were divided with respect to high body fat (HF; 18-22%, n = 12) or low body fat (LF; 8-12%, n = 12) and randomly assigned to one of three water temperatures. Body heat debt and R did not differ between the LF or HF groups, between temperatures, or across time. Percent calories utilized indicated that for these experimental conditions the predominant substrate utilized between the LF and HF groups across time was derived from carbohydrate. In addition, VO2 was greater (p = .0004) in the LF than HF group, and the latter was greater (p = .0013) in the 18 degrees C group versus the 26 degrees C group and increased across time (p = .0001); that is, VO2 after 5 min of immersion was less than at 60 and 90 min, and values obtained after 30 min of immersion were less than those at 90 min of immersion. Based on these data, it appears that the LF group would expend more calories (308.9 vs. 199.9 kcal, respectively) and more likely derive these calories from a carbohydrate source than the HF group during 90 min of cold water immersion. It would appear beneficial to consider a feeding supplement for the low-fat individual if immersion was in a more thermal stressful environment or extended for a protracted period of time.

Adipose Tissue↗

PubMed1986

Increasing incidence of childhood immersion injury in Brisbane.

The incidence of childhood immersion injury in a defined population is reported. The data were drawn from this Hospital's Child Injury Surveillance programme and cover the period July 1, 1984 to June 30, 1985. The overall rate of immersion injury was 26.8 per year per 100 000 children at risk and the rate for fresh-water immersions was 25.3. The magnitude of this public health problem is revealed by an annual fresh-water immersion rate of 70.2 per 100 000 at risk for the critical 0 to four years' age group. Eighty per cent of all immersions occurred in swimming-pools and the rate of pool immersion is three times that reported in the Brisbane Drowning Study (1971-1975). Eighty per cent of immersions in back yard pools were potentially avoidable by the provision of an effective safety barrier. Only 25% of the families that were involved could be described as being familiar with their pool.

Adolescent↗

PubMed1976

Deconditioning during prolonged immersion and possible countermeasures.

Test subjects covered with a waterproof highly elastic cloth were exposed to 13-day water immersion up to the neck. They were divided into two groups. The first (control) group consisting of six persons was exposed to immersion alone and the second (experimental) group was exposed daily to accelerations of 0.6-2 Gz for 60-90 min during the last 6 days of immersion. Before and after immersion all the test subjects were exposed to +3 Gz for 5 min which served as a provocative test. These experiments give evidence that the use of dry immersion allows experimentation during prolonged immersion without concomitant complications. Variations in the physiological parameters (cardiovascular system, fluid-electrolyte balance, blood-coagulatory system) are indicative of the preventive effect of periodic accelerations during 13-day immersion.

Acceleration↗

PubMed1990

The effect of clothing on the initial responses to cold water immersion in man.

The protection provided by three clothing assemblies against the cold shock response was investigated. Nine healthy male volunteers each undertook three two minute head-out immersions into stirred water at 10 degrees C. The subjects wore a different clothing assembly for each immersion, these were: a) Swimming trunks only; b) Conventional clothing (equivalent to RN No 8s); c) Conventional clothing plus windproof/shower-proof clothing (RN foul-weather clothing Mk III). The cardiac, ventilatory and thermal responses of the subjects were examined before and during the immersions. No significant differences were found between the magnitude of the responses recorded on immersion when conventional clothing or foul-weather clothing were worn. Mean skin temperature was lower (P less than 0.05) and respiratory frequency and minute ventilation were higher (P less than 0.05) on immersion in swimming trunks compared to the other two conditions. It is concluded that when policies for the use of immersion protective clothing are being formulated, consideration should be given to all of the potentially hazardous responses associated with cold water immersion.

Adult↗

PubMed1989

Hyperventilation response to cold water immersion: reduction by staged entry.

Staged immersion of humans into cold water was investigated to determine whether the hyperventilation response could be reduced by this behavioral technique. A simple, two-stage procedure involving immersion to the waist for 30 s before full immersion to neck level was compared to non-staged immersion. For the staged immersion, maximum values of respiratory minute volume and respiratory frequency were significantly reduced by 35% and 38%, respectively, from the maxima observed for non-staged immersion. These results indicate that if staged immersion into cold water is possible, it can attenuate the hyperventilation response and, therefore, the probability of sudden drowning. We recommend that this knowledge be incorporated into teaching programs concerning cold water safety.

Adult↗

PubMed1987

The influence of regional insulation on the initial responses to cold immersion.

Twelve healthy male subjects performed three 10-min head-out immersions in water at 10 degrees C. The responses of the subjects to immersion were recorded under three conditions: a) Control condition (CC)--torso and limbs exposed; b) Torso protected/limbs exposed condition (TPC); and c) Limbs protected/torso exposed condition (LPC). Results showed that the LPC significantly reduced the heart rate (p less than 0.01), minute ventilation (p less than 0.05), and respiratory frequency (p less than 0.05) during the first minute of immersion compared to the CC. Subjects also found the LPC the most comfortable. The TPC significantly reduced minute ventilation (p less than 0.01) and respiratory frequency (p less than 0.01) on immersion compared to the CC, but did not significantly lower the heart rate response. A comparison of the LPC and TPC revealed no significant difference in minute ventilation and respiratory frequency recorded on immersion. The LPC however, produced significantly lower heart rates on immersion (p less than 0.05) than the TPC. It was concluded that the limbs may be more important than the torso for the initiation of cardiac response to cold water immersion.

Adult↗

PubMed1987

Pulmonary mechanics and atelectasis during immersion in oxygen-breathing subjects.

It has been suggested that vital capacity (VC) reduction seen during head-out immersion and oxygen breathing is due to atelectasis formation. In this study VC was reduced in 8 healthy subjects by 8.7% as an effect of immersion per se and by a further 14.3% as an effect of oxygen breathing during 30 min of immersion. Every 2nd min during the exposure, functional residual capacity (FRC), dynamic compliance (C-dyn), and static esophageal pressure at end-expiration (Pes-frc) were measured by body plethysmographic technique. Results were compared with an air-breathing, immersed control situation to evaluate any possible atelectasis formation. The only significant changes during immersion were observed after 30 min of air breathing, where FRC decreased linearly by 8.5% and C-dyn by 13.2%. The main conclusion is that atelectases acting solely as volume restrictors cannot explain the whole VC reduction without other additive or synergistic mechanisms. We suggest that the linear decrements in FRC and C-dyn as an effect of immersion time might be explained by either inspiratory muscle fatigue or increasing thoracic fluid compartment during the first 30 min of head-out immersion.

Adult↗

PubMed1979

Comparison of physiological effects of head-down tilting and immersion on the human body.

Among the methods simulating weightlessness, effects on the human body, head-down tilting and water immersion are very useful. The purpose of the present investigation was to carry out a comparative study of water balance and water-protein composition of the blood using the above two methods to simulate the physiological effects typical of an acute stage of weightlessness adaptation. The results of the 7-d head-down tilting and immersion experiments allow the following conclusions: More pronounced changes in water balance and water-protein composition of the blood during immersion seem to indicate that immersion produces a greater effect on the human body; The pattern of changes during immersion and tilting suggests that the adaptation period to immersion takes a longer time; These findings give evidence that immersion, compared with head-down tilting, reproduces more closely effects of acute adaptation to simulated weightlessness.

Adaptation, Physiological↗

PubMed1978

Influence of hydrostatic compression of the chest and intrathoracic blood pooling on static lung mechanics during head-out immersion.

The effect of water immersion on static lung volumes and pressure-volume curves was studied in five subjects. A special container allowed measurements during nonimmersion, head-out immersion, and thorax immersion leaving the head, pelvis region, and legs dry. It was thus possible to separate the part played by hydrostatic forces acting on the chest from the part played by intrathoracic blood pooling during immersion. Hydrostatic compression of the chest decreased total lung capacity (TLC) by 0.30 liter and residual volume (RV) by 0.25 liter. Blood redistributed into the thorax during head-out immersion caused a further reduction of TLC of 0.13 liter; RV increased by 0.10 liter, probably because expiration was hampered by air-trapping. Heal-out immersion reduced VC by 0.29 liter compared to nonimmersion, and this effect was wholly attributable to intrathoracic blood pooling. Lung compliance during head-out immersion was 0.11 liter x (cmH2O)-1 smaller than during nonimmersion; this was mainly due to intrathoracic blood pooling. Results support the notion that blood redistribution decreased lung compliance by exerting an erectile effect on the lung tissue.

Adult↗

PubMed1984

Effects of head-out water immersion on the urinary excretion of phosphate, calcium and magnesium in the awake dog.

The present study was undertaken to define the effects of heat-out water immersion on the urinary excretion of phosphate (UPO4V), calcium (UCaV), and magnesium (UMgV) in the awake dog. 53 dogs were divided into three groups: group I, time-control, from 10 a.m. to 4 p.m.; group II, immersion for 2 h, studied from 10 a.m. to 4 p.m., and group III, immersion for 2 h, studied from 4 p.m. to 10 p.m. Our results show that head-out water immersion did not alter the spontaneous pattern of UPO4V. When immersion was performed from 1 p.m. to 3. p.m. (group II), it had no effect on UCaV but induced a significant increase in UMgV although fractional excretion of Mg (FEMg) remained unchanged. When immersion was performed from 7 p.m. to 9 p.m. (group III), however, both UCaV and UMgV increased significantly. FECa also increased significantly in this group but FEMg again remained unchanged. The changes in UCaV were dissociated with UNaV. Changes in plasma PO4 (PPO4) and arterial pH were unrelated to changes in UCaV or UPO4V. Our findings show that head-out water immersion induces significant increases in UCaV and UMgV by mechanisms which are independent of parathyroid hormone (PTH) or acid base changes. The rise in UMgV seems to be related to an increase in the filtered load, while the increases in UCaV are secondary to changes in the renal tubular handling of calcium. Thus, under these experimental circumstances, Ca and Mg reabsorption seem to occur via different distal tubular pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1978

Effects on handgrip strength due to arm immersion in a 10 degree C water bath.

Thirteen male and female human subjects participated in an experiment to determine if cold water immersion of the arm increases post-immersion handgrip strength. The test involved immersion of a subject's fore-arm into a 10 degrees C water bath for 30 min once a week in a 3-week series, involving a control test and two immersion experiments. Handgrip strength was measured 20 min before and then once every 20 minutes after the cold bath immersion for 4 h, for a total of 18 readings. Grip strength significantly decreased as a consequence of immersion of the forearm. However, strength recovery to approximately normal values took place within 40 min. No increases in post-immersion strength were observed.

Adult↗

PubMed1995

Immersion fatalities: hazardous responses and dangerous discrepancies.

In this paper the following question is addressed: 'Why, given the plethora of standards, specifications and guidelines for immersion protective equipment, are lives still being lost at sea and fatal accident enquiries questioning the quality of such equipment?' In attempting to answer this question, consideration is given to the extent to which both the possible prevailing environmental conditions, and the physiological responses they evoke, are recognised in the design, selection and evaluation of immersion protective equipment. The hazardous responses associated with immersion in cold water are briefly reviewed and the value and relevance of some of the existing tests of immersion protective clothing are considered. It is concluded that: i. when standards, policies and tests for the selection and use of immersion protective clothing are being formulated, consideration should be given to all of the hazardous responses associated with immersion; ii. it should be recognised that the performance of immersion protective equipment during an accident may be significantly inferior to that predicted by routine testing for certification.

Cold Temperature↗

PubMed1993

Effect of task complexity on mental performance during immersion hypothermia.

The effect of task complexity on the decrement in mental performance during immersion hypothermia was studied. Psychometric tests of varying length and complexity were administered: 1) prior to cold water immersion (baseline); 2) soon after immersion to the neck in cold (8 degrees C) water but prior to any decrease in core temperature; and 3) after 55 to 80 min of immersion when core temperature had decreased 2-4 degrees C. Results indicated that tests placing relatively minimal cognitive demands on individuals, such as auditory attention, the Benton visual recognition test and forward digit span, were unaffected by either initial cold water immersion or central cooling. On the other hand, tests requiring relatively greater mental manipulation and short term memory (i.e., backward digit span) or processing and analysis (i.e., Stroop test) showed a slight improvement upon cold water immersion (perhaps related to increased arousal and/or learning) but a significant decrement following central cooling of 2-4 degrees C. Thus, relatively simple tasks were unaffected by central cooling, whereas more complex tasks were adversely affected. Cold water immersion itself did not interfere with performance of any tasks. Central nervous system cooling probably interferes with mental processing although discomfort and/or the physiological and physical effects of cold on the neuromuscular aspects of speech, required for responses to some of the tasks, may also affect performance.

Adult↗

PubMed2004

Performances of high numerical aperture water and oil immersion objective in deep-tissue, multi-photon microscopic imaging of excised human skin.

Multi-photon fluorescence microscopy (MPFM) is a powerful technique for imaging scattering, biological specimens in depth. In addition to the sectioning effect generated by the point-like excitation volume, the near-infrared wavelengths used for multi-photon excitation allow deeper penetration into optically turbid specimens. In physiological specimens, the optical properties such as the scattering coefficients and refractive indices are often heterogeneous. In these specimens, it is not clear which type of immersion objective can provide optimized images in-depth. In particular, in-depth dermatological imaging applications using MPFM requires such optimization to obtain qualitative and quantitative information from the skin specimens. In this work, we address this issue by comparing the performances of two common types of high numerical aperture (NA) objectives: water-immersion and oil-immersion. A high-quality water-immersion objective (Zeiss, 40 x C-Apochromat, NA 1.2) and a comparable oil-immersion objective (Zeiss, 40 x Fluar, NA 1.25) were used for in-depth imaging of autofuorescent excised human skin and sulforhodamine B treated human skin specimens. Our results show that in the epidermal layers, the two types of immersion objectives perform comparably. However, in the dermis, multi-photon imaging using the oil immersion objective results in stronger fluorescence detection. These observations are most likely due to the degraded point-spread-function (PSF) caused by refractive index mismatch between the epidermis and the dermis.

Dermis↗