PubMed Health⌕ Search

Biomedical subjects

M J Tipton

Publications and source records attributed to M J Tipton.

At least 19 recordsLinked to original sources
PubMed1998

Habituation of the initial responses to cold water immersion in humans: a central or peripheral mechanism?

1. The initial respiratory and cardiac responses to cold water immersion are thought to be responsible for a significant number of open water deaths each year. Previous research has demonstrated that the magnitude of these responses can be reduced by repeated immersions in cold waterwhether the site of habituation is central or peripheral. 2. Two groups of subjects undertook two 3 min head-out immersions in stirred water at 10 C of the right-hand side of the body (R). Between these two immersions (3 whole days) the control group (n = 7) were not exposed to cold water, but the habituation group (n = 8) undertook a further six 3 min head-out immersions in stirred water at 10 C of the left-hand side of the body (L). 3. Repeated L immersions reduced (P < 0.01) the heart rate, respiratory frequency and volume responses. During the second R immersion a reduction (P < 0.05) in the magnitude of the responses evoked was seen in the habituation group but not in the control group, despite both groups having identical skin temperature profiles. 4. It is concluded that the mechanisms involved in producing habituation of the initial responses are located more centrally than the peripheral receptors.

Adolescent↗
PubMed1998

Temperature dependence of habituation of the initial responses to cold-water immersion.

The initial responses to cold-water immersion, evoked by stimulation of peripheral cold receptors, include tachycardia, a reflex inspiratory gasp and uncontrollable hyperventilation. When immersed naked, the maximum responses are initiated in water at 10 degrees C, with smaller responses being observed following immersion in water at 15 degrees C. Habituation of the initial responses can be achieved following repeated immersions, but the specificity of this response with regard to water temperature is not known. Thirteen healthy male volunteers were divided into a control (C) group (n = 5) and a habituation (H) group (n = 8). Each subject undertook two 3-min head-out immersions in water at 10 degrees C wearing swimming trunks. These immersions took place at a corresponding time of day with 4 days separating the two immersions. In the intervening period the C group were not exposed to cold water, while the H group undertook another six, 3-min, head-out immersions in water at 15 degrees C. Respiratory rate (fR), inspiratory minute volume (VI) and heart rate (fH) were measured continuously throughout each immersion. Following repeated immersions in water at 15 degrees C, the fR, VI and fH responses of the H group over the first 30 s of immersion were reduced (P < 0.01) from 33.3 breaths x min(-1), 50.5 l x min(-1) and 114 beats x min(-1) respectively, to 19.8 breaths x min(-1) 26.41 x min(-1) and 98 beats x min(-1), respectively. In water at 10 degrees C these responses were reduced (P < 0.01) from 47.3 breaths x min(-1), 67.61 x min(-1) and 128 beats x min(-1) to 24.0 breaths x min(-1), 29.5 l x min(-1) and 109 beats x min(-1), respectively over a corresponding period of immersion. Similar reductions were observed during the last 2.5 min of immersions. The initial responses of the C group were unchanged. It is concluded that habituation of the cold shock response can be achieved by immersion in warmer water than that for which protection is required. This suggests that repeated submaximal stimulation of the cutaneous cold receptors is sufficient to attenuate the responses to more maximal stimulation.

Adaptation, Physiological↗
PubMed1997

The effect of blood alcohol on the initial responses to cold water immersion in humans.

Many drowning victims have alcohol in their blood, but it is not clear whether there is a causal relationship. This study examined the effect of moderate alcohol consumption on the initial responses to cold water immersion. Sixteen subjects wearing swimming costumes undertook two, 3-min head-out seated immersions in water at 15 degrees C. One hour before immersion, subjects drank either 3.7 ml.kg body water-1 of 40% v:v alcohol as vodka, or an equivalent volume of water (control) mixed with squash. On immersion, the average blood alcohol concentration was 23 mmol.l-1 (105 mg.100 ml-1) after alcohol consumption and zero in the control condition. Respiratory frequency in the first 20 s of immersion was found to be reduced (P < 0.05) by 10% (a total of 2-3 breaths) after alcohol consumption compared to the control immersion. Tidal volume, heart rate, rectal temperature and skin temperatures did not differ significantly between immersions. It is concluded that moderate alcohol consumption does not attenuate the initial "cold shock" responses to a practically significant extent and is thus unlikely to reduce the risk of drowning on immersion in cold water.

Adult↗
PubMed1997

Substrate utilisation during exercise and shivering.

It is generally assumed that exercise and shivering are analogous processes with regard to substrate utilisation and that, as a consequence, exercise can be used as a model for shivering. In the present study, substrate utilisation during exercise and shivering at the same oxygen consumption (VO2) were compared. Following an overnight fast, eight male subjects undertook a 2-h immersion in cold water, designed to evoke three different intensities of shivering. At least 1 week later they undertook a 2-h period of bicycle ergometry during which the exercise intensity was varied to match the VO2 recorded during shivering. During both activities hepatic glucose output (HGO), the rate of glucose utilisation (Rd), blood glucose, plasma insulin, free fatty acid (FFA) and beta-hydroxybutyrate (B-HBA) concentrations were measured. The VO2 measured during the different levels of shivering averaged 0.49 l.min-1 (level 1: low), 0.6 l.min-1 (level 2: low-moderate), and 0.9 l.min-1 (level 3: moderate), and corresponded closely to the levels measured during exercise. HGO and Rd were greater (P < 0.05) during exercise than during shivering at the same VO2 (9.5% and 14.7%, respectively). The average (SD). HGO during level 3 exercise was 3.0 (0.91) mg.kg-1.min-1 compared to 2.76 (1.0) mg.kg-1.min-1 during shivering. The values for Rd were 3.06 (0.98) mg.kg-1.min-1 during level 3 exercise and 2.68 (0.82) mg.kg-1.min-1 during shivering. Blood glucose levels did not differ between conditions averaging 5.4 (0.3) mmol.l-1 over all levels of shivering and 5.2 (0.3) mmol.l-1 during exercise. Plasma FFA and B-HBA were higher (P < 0.01) during shivering than during corresponding exercise (12.3% and 33.3%, respectively). FFA averaged 0.61 (0.2) mmol.l-1 over all levels of shivering and 0.47 (0.16) mmol.l-1 during exercise. The figures for L-HBA were 0.44 (0.13) mmol. l-1 during all levels of shivering and 0.32 (0.1) mmol.l-1 during exercise. Plasma insulin was higher (P < 0.05) during level 2 and 3 shivering compared to corresponding exercise; at these levels the average value for plasma insulin was 95.9 (21.9) pmol.l-1 during shivering and 80.6 (16.1) pmol.l-1 during exercise. On the basis of the present findings it is concluded that, with regard to substrate utilisation, shivering and exercise of up to 2 h duration should not be regarded as analogous processes.

3-Hydroxybutyric Acid↗
PubMed1997

An examination of two emergency breathing aids for use during helicopter underwater escape.

BACKGROUND: There is a paucity of published work in which the performance of Emergency Underwater Breathing Aids (EUBA) has been examined in the wide range of scenarios in which helicopter underwater escape may be necessary. In the present investigation two EUBA were examined: the Air Pocket (AP) rebreather and the Short Term Air Supply System (STASS) mini SCUBA set. METHOD: Young, healthy male subjects undertook simple simulated helicopter underwater escapes in water at 15 degrees C and/or 5 degrees C. During the immersions the subjects attempted to remain submerged for 60 s while traversing back and forth along a ladder secured at a depth of 1.25 m. At each temperature the subjects used AP and STASS twice. The subjects were dressed in the Royal Navy winter sea helicopter aircrew equipment assembly and an aircrew helmet. RESULTS: Both AP and STASS significantly extended the underwater survival time of individuals when compared to their maximum breath-hold time (BHT). It is clear from the measurements made of gas concentrations in AP; the volume of air used from STASS; and subjective responses, that the 60-s submersions were achieved more easily with STASS than AP. CONCLUSION: It is concluded that in conditions similar to those of the present experiment STASS will give a longer underwater duration than AP, but this benefit must be offset against the possible risk of pulmonary barotrauma associated with the use of STASS, as well as increased training and maintenance costs. Irrespective of the EUBA which is provided, in-water training, preferably including exposure to cold water, will significantly improve the ability of an individual to use it.

Accidents, Aviation↗
PubMed1996

The effect of water leakage on the results obtained from human and thermal manikin tests of immersion protective clothing.

The effect of both the volume and location of water leakage on the protection provided by an uninsulated immersion suit was investigated using human subjects and, in corresponding experiments, an immersion thermal manikin. Three volumes of "leakage" to the torso (200, 500 and 1000 ml) were examined, as were two conditions in which no leakage was simulated and one condition in which a 500-ml leak to the limbs was simulated. All leakages were introduced in a standardised way before immersion. The measurements of clothing insulation obtained, both from the manikin and the humans, were in general agreement. The human experimentation provided some support for a 200-ml limit to water leakage in tests of immersion suits. Rectal and aural temperatures remained significantly (P < 0.05) higher when a 500-ml leak was applied to the limbs rather than the torso; this was primarily due to greater heat flow through and from the torso (back) during the immersions with torso wetting. The physiological responses and anthropometric characteristics which determine this response are not present in manikins; the implications of this for the application and design of immersion thermal manikins, as well as the protection of those at risk of immersion in cold water, are discussed. It is concluded that using immersion thermal manikins to provide a single overall measure of clothing insulation will not necessarily distinguish between suits which provide quite different levels of protection for humans.

Body Temperature↗
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↗
PubMed1995

An evaluation of hand immersion for rewarming individuals cooled by immersion in cold water.

The hypothesis that hypothermic individuals can be actively rewarmed in the field by immersion of the extremities in hot water was investigated. Three techniques for rewarming subjects with lowered deep body temperatures were compared: a) whole body immersion to the neck in water at 40 degrees C; b) immersion of two hands plus forearms only in water at 42 degrees C; and c) passive rewarming. The suggestion that the fall in deep body temperature resulting from immersion to the neck in water at 15 degrees C could be arrested by immersing both arms in water at 42 degrees C was also investigated. Results indicated that immersion to the neck in hot water was clearly the most effective rewarming technique. No significant difference (p > 0.05) was observed in the deep body temperature response during passive rewarming or during immersion of both hands and forearms in water at 42 degrees C. In the later condition some increase in peripheral blood flow to the hands may have occurred and resulted in a heat input of approximately 12 W, but any benefit from this was negated by an associated significant decrease (p > 0.05) in intrinsic heat production. Immersing the arms in hot water during immersion to the neck in cold water appeared to accelerate rather than decelerate the rate of fall of deep body temperature. We concluded that hand rewarming, although theoretically attractive, is ineffective in practice and could be detrimental in some circumstances, by suppressing intrinsic heat production or precipitating rewarming collapse.

Adult↗
PubMed1995

A simple emergency underwater breathing aid for helicopter escape.

Experiments were undertaken to determine whether a simple rebreathing system, termed "Air Pocket" (AP), could, when integrated into an immersion dry suit, extend the underwater survival time of individuals when compared with their maximum breath hold time (BHTmax). Eight naive healthy male subjects undertook a series of resting submersions and simulated simple helicopter underwater escapes in water 25 degrees C and 10 degrees C. During the submersions the subjects breath-held maximally and then rebreathed using an otherwise empty AP. the BHTmax times of subjects and the total time they could remain underwater (RBT) were recorded. The results showed that the ability to rebreathe following a BHTmax extended the time all subjects could remain submerged, resting or exercising, in cold water by a factor of at least two. The average BHTmax during simulated helicopter underwater escapes in the cold water was 17.2 s. It is concluded that the ability of subjects to rebreathe immediately following maximum breath holding extends the time they can remain submerged in cold water to as much as 60 s. Further, if used unprimed, a simple rebreathing system will not introduce any additional dangers such as a pulmonary over-pressure accident.

Aircraft↗
PubMed1994

The effects of warming by active and passive means on the subsequent responses to cold water immersion.

Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15 degrees C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (Tre) rose by an average of 0.73 degree C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40 degrees C) until their Tre rose by an average of 0.9 degrees; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35 degrees C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of Tre during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46 degrees C.h-1) compared with the control condition (1.68 degrees C.h-1). However, this rate was observed when absolute Tre was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (Tau) seen in experiment 1 and the Tau and Tre in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI.

Adult↗
PubMed1994

Supraventricular arrhythmias following breath-hold submersions in cold water.

Twelve subjects undertook one submersion into water at 5 degrees C and two at 10 degrees C wearing either a wet or dry suit. During the submersions the subjects held their breath for as long as they could and then breathed through respiratory tubing for a further 10 s before being removed from the water. Bradycardia (heart rate < 60 beats/min) was observed during breath holding in 10 subjects in 28 of the 36 submersions. Ectopic arrhythmias were observed in 11 subjects in 29 of the 36 submersions, a much higher frequency than previously reported. These ectopic arrhythmias included premature atrial and junctional complexes, runs of supraventricular tachycardia, and premature ventricular complexes. They occurred predominantly in the 10-s period of submersion after the cessation of breath holding. The possible etiology of these arrhythmias and their significance are discussed and it is concluded that after breath-hold termination during cold-water submersion there is a short time during which the heart may be particularly susceptible to supraventricular ectopic arrhythmias.

Adult↗
PubMed1993

Hand immersion as a method of cooling and rewarming: a short review.

Many cooling and warming procedures have been proposed for the treatment of hyperthermic or hypothermic individuals. One of the most recent of these is the use of hand immersion as a simple method to gain or lose heat. In the present paper the principles underlying this approach, and the evidence for and against hand rewarming/cooling, are briefly reviewed. It is concluded that hand immersion is likely to be more effective for cooling than rewarming individuals.

Cold Temperature↗
PubMed1993

The concept of an 'Integrated Survival System' for protection against the responses associated with immersion in cold water.

In this paper the concept of an 'Integrated Survival System' (ISS) is introduced and discussed in relation to the helicopter passenger/crew member, although the principles are equally applicable to many other types of user and circumstance requiring specialized protective clothing. The fundamental principles behind this concept are first, that the wearer should be given protection against all of the hazardous responses associated with immersion in cold water and secondly, that the individual components which make up the ISS must be compatible and complementary; they may also be interdependent.

Accidents, Aviation↗
PubMed1992

The relationship between maximum breath hold time in air and the ventilatory responses to immersion in cold water.

Eight subjects performed maximum breath holds in air and naked head-out immersions of 2 min duration in stirred water at 5, 10 and 15 degrees C. Analysis of the respiratory data collected in air and on immersion revealed a significant (P less than 0.05) inverse relationship between the maximum breath hold time (tbh,max) of subjects in air and their frequency of breathing and inspiratory volumes on immersion. No such relationship was identified between tbh,max in air and tidal volumes on immersion. It is concluded that the tbh,max of individuals in air may provide an indication of the magnitude of some of their respiratory responses to immersion. This information may be of use when personnel are being selected for activities with a high risk of immersion in cold water.

Adult↗
PubMed1991

Laboratory-based evaluation of the protection provided against cold water by two helicopter passenger suits.

The thermal protection provided by two helicopter passenger immersion suits was evaluated. Suit A was a standard 'dry' suit and suit B was a 'dry' suit with inherent insulation provided by inflation of the outer shell of the suit. During four hour immersions in water at 4 degrees C with simulated rain, wind and waves, suit B provided significantly (p less than 0.01) better protection against the long-term effects of immersion than suit A. The skin and core temperature of subjects fell at slower rates over the immersion period when they wore suit B, they shivered less, had lower heart rates and were more comfortable in this suit. The problems of testing and selecting appropriate immersion suits are discussed and it is concluded that tests of immersion suits should be as realistic as possible and, when this is so, 'dry' suits with inherent insulation which is unaffected by leakage are likely to perform better in cold water than those without such insulation.

Aircraft↗
PubMed1991

Human initial responses to immersion in cold water at three temperatures and after hyperventilation.

The present investigation was designed to examine the influence of water temperature and prior hyperventilation on some of the potentially hazardous responses evoked by immersion in cold water. Eight naked subjects performed headout immersions of 2-min duration into stirred water at 5, 10, and 15 degrees C and at 10 degrees C after 1 min of voluntary hyperventilation. Analysis of the respiratory and cardiac data collected during consecutive 10-s periods showed that, at the 0.18-m/s rate of immersion employed, differences between the variables recorded on immersion in water at 5 and 10 degrees C were due to the duration of the responses evoked rather than their magnitude during the first 20 s. The exception to this was the tidal volume of subjects, which was higher on immersion in water at 15 degrees C than at 5 or 10 degrees C. The results suggested that the respiratory drive evoked during the first seconds of immersion was more closely reflected in the rate rather than the depth of breathing at this time. Hyperventilation before immersion in water at 10 degrees C did not attenuate the respiratory responses seen on immersion. It is concluded that, during the first critical seconds of immersion, the initial responses evoked by immersion in water at 10 degrees C can represent as great a threat as those in water at 5 degrees C; also, in water at 10 degrees C, the respiratory component of this threat is not influenced by the biochemical alterations associated with prior hyperventilation.

Adult↗