Ash, humans to remain submerged in water and

  

 Ash, S. (2015).

DIVING
REFLEX PRACTICAL

WORD
COUNT:2000

ANNIE
OMOREGIE (U1674367) | PHYSIOLOGY: CONTROL AND COORDINATION | 14/12/2017

INTRODUCTION

Diving
reflex is a physiological mechanism that allows animals including humans to
remain submerged in water and it comprises of three independent reflexes that
cause physiological changes that counter homeostatic control (Michael
Panneton, W. 2013) and they are bradycardia which is the slowing down of the
heart rate, peripheral vasoconstriction, and hypertension. It is a very
powerful collection of reflexes that allow the preservation of oxygen for
aerobic metabolism and function of the heart and brain (Panneton, W. M., Gan, Q.,
& Juric, R. 2010). Aquatic and marine mammals such as sea otters,
platypus, hippotamus, whales, dolphins, and seals exhibit this reflex as they
can remain submerged for extended periods of time (Hempleman, H. V., &
Lockwood, A. P. M. 1978) because they are able to conserve oxygen as a means of
survival, this is the main physiological purpose of the diving reflex. The
level at which humans use this reflex is limited in terms of time compared to
the aquatic and marine mammals as they can’t remain submerged for long periods
of time. The aim of the diving reflex practical is to assess the cardiovascular
changes in heart rate and mean arterial pressure during simulated diving in
different conditions to identify the key stimuli for the diving reflex. It was
therefore hypothesized that facial immersion in water will lead to a decrease
in heart rate and an increase in mean arterial pressure, if so what effect does
the temperature of the water have on the extent of the diving reflex in humans.

METHOD

PARTICIPANTS

Twenty
healthy participants in groups of two, aged 19-25 years took part in the
experiment voluntarily after signing a consent form which was in line with the
Health and Safety guidelines of the School of Applied Sciences, University of
Huddersfield.

Experimental
Procedure

Heart
rate, systolic and diastolic pressure were measured using a blood pressure (BP)
monitor during each of the conditions. The cuff of the monitor was positioned
on the right arm at the same level as the heart for each participant and the
participants were seated comfortably upright and breathing normally before the
rest reading was taken twice to ensure a steady heart rate and blood pressure
at the start of the investigation. The first condition required the
participants to hold their breath in air until a BP/HR reading is obtained, the
second condition required the participants to submerge their faces in warm
water at 25?c after a 5 minutes’ rest to allow the participant’s cardiovascular
values return to a steady baseline. Their faces are kept submerged until a
reading is obtained. The same procedure is carried out in the third condition
except that the temperature of the water is 10?c. A bowl, towel, thermometer
and tap water were required for the experiment.

Data
Analysis

Data
analysis was carried out using the Statistical Package for the Social Sciences
(SPSS). Normality tests and descriptive analysis which included the measures of
central tendency and variability were used to describe the results of the four
conditions the participants were subjected to. To test the hypothesis, the
repeated measures ANOVA test was used to compare and test the differences
between the results of the conditions. The same participants were used throughout
the experiment and the conditions and results are related also the data fit the
assumptions necessary to run the repeated measures ANOVA (Laerd
Statistics. Lund Research Ltd. 2013). The Mauchly’s test of Sphericity was used to test for
unequal variances between all the combinations of the conditions as a violation
of this would make the repeated measures ANOVA to become too flexible (Laerd
Statistics. Lund Research Ltd. 2013).

RESULTS

Results from the normality test and graphical representation of the
frequency distribution of the heart rate and mean arterial pressure during each
condition suggested that the data was parametric because the data samples were
<50 the Shapiro-Wilk tests of normality was considered and the significance in each case was greater than 0.05. For the sake of clarity, the two cardiovascular responses will be evaluated separately. HEART RATE The table and graph below show the results of the descriptive analysis of the class result for the effect of the diving reflex on heart rate. CONDITION MEAN HEART RATE STANDARD DEVIATION STANDARD ERROR At rest 77.389 7.2877 2.429 Holding breath 70.222 8.8991 2.966 Warm water 67.667 6.1237 2.041 Cold water  64.000 7.5333 2.511 The mean heart rate does decrease with facial immersion in water and decreases further in cold water but we cannot conclude based on the graph hence to test if the difference shown on the graph is significant. The Mauchly's test of Sphericity gave a significance of 0.72 p<0.05 hence the data did not violate sphericity. A repeated measures ANOVA with no correction resolved that the mean heart rate is statistically different (F (3,24) =7.465, p<0.05. To determine where the differences occurred a Bonferroni post hoc test resulted in a pairwise comparisons table (appendix) which revealed that holding one's breath which reduced heart rate was not  statistical different on the heart rate when at rest, in cold water and warm water conditions (p=0.363,p=1.0 and p=1.0 respectively) also the difference between the mean heart rates in warm and cold water conditions had a statistically significant difference from rest (p=0.016 and p=0.001 respectively). There were no statistically significant differences between the effect of warm and cold water had on heart rate p=0.928. MEAN ARTERIAL PRESSURE (MAP) The mean arterial pressure was calculated from the systolic and diastolic pressures recorded with the formula MAP=(SBP+2DBP/3). The table and graph below summarize the results of the descriptive analysis. CONDITION MEAN MAP STANDARD DEVIATION STANDARD ERROR At rest 91.711 14.3693 4.790 Holding breath 92.522 15.4061 5.135 Warm water 103.256 17.7004 5.242 Cold water 115.467 15.7265 5.900 The graph clearly shows that the mean arterial pressure increases with facial immersion in water also the pressure is higher in cold water than in warm. The data did not violate the assumption of sphericity 0.92 p<0.05 and the repeated measures ANOVA showed that the data the difference is statistically significant (F (3,24) =12.046) p<0.05. the post hoc test proves that the mean arterial pressure measured in cold water conditions has a significant statistical difference from the other conditions (p=0.008 at rest, p=0.000 holding breath and p=0.046 warm water). The other conditions did not exhibit any significant statistical difference from the MAP at rest. DISCUSSION/CONCLUSION The results show a difference between the heart rate and mean arterial pressure during rest and apnea (holding breath) but the test suggests that the difference is not statistically significant. Although this may be the case of this experiment previous experiments concluded that apnea is necessary to the diving reflex to prevent the inhalation of water (Ansay, M. et al. 2016) but the effect on the cardiovascular output are minimal (Gooden, B. A. 1994). The slight difference in cardiovascular output may because the participant is consciously preventing oxygen uptake which pushes the body to conserve oxygen, the chemoreceptors are stimulated by the rising CO2 levels in the bloodstream causing the sympathetic nervous system to stimulate vasoconstriction and the parasympathetic system to decrease the heart rate (Dampney, R. A. L. 2016).Compared to holding breath the changes in the cardiovascular outputs during facial immersion is statistically significant because direct facial contact with water stimulates the diving reflex (Foster, G. E., & Sheel, A. W. 2005). Facial immersion in water stimulates both the thermoreceptors and mechanoreceptors to detect moisture (Columbia Chronicle. 2014). These receptors relay the message to the brain via the parasympathetic vagus nerve where the respiratory center stimulates a reflex apnea and bradycardia (Michael Panneton, W. 2013), while the trigeminal nerve activates the sympathetic nervous system to cause peripheral vasoconstriction which increases the blood pressure. The temperature of the water also has a role to play in accentuating the diving reflex as the results reveal that the difference between the decrease heart rate and increase in mean arterial pressure compared to warm water is significant but it is not a stimuli for the diving reflex because a localized cold stimulus to the face increases mean arterial pressure via the trigeminal nerve hence it only represents a fraction of the response to diving (Brown, C. M., Sanya, E. O., & Hilz, M. J. 2003). A decrease in temperature is detected by the cold receptors on the face which triggers the activity of the sympathetic nervous system to cause skin vasoconstriction and hair rising to increase skin insulation and the release of norepinephrine and epinephrine which leads to peripheral vasoconstriction of the blood vessels and increased blood pressure. the reverse is for warm water which is detected by the warmth receptors on the face causes vasodilation of the blood vessels and reduced blood pressure (Dampney, R. A. L. 2016). The diving reflex applies the spinothalamic pathway because it employs the use of different receptors (thermoreceptors and mechanoreceptors) to elicit, pressure and temperature sensations (Greenhough, K. 2017) that are transmitted via the trigeminal nerve to the thalamus for central processing and finally the response is relayed through the vagus nerve which innervates the heart to carry out the parameters measured in the experiment. (Singh, G.P. & Chowdhury, T. 2017) The diving reflex shares similarities with the trigeminal-cardiac reflex which it is a subtype of, but what differs between the two is the effect on blood pressure. While the trigeminal-cardiac reflex causes blood pressure to increase the diving reflex does the opposite. This is due to the sympathetic stimulation during diving (Singh, G.P., et al. 2016) caused by the rising CO2 levels in the blood when holding breath. This effects on the heart are carried out by the beta-adrenoreceptors and muscarinic receptors (Klabunde, R.E. 2016). Further changes that can occur as a result of the maximal diving reflex are the contraction of the spleen and blood shift. Splenic contraction releases more red blood cells hence increasing the hemoglobin content in circulation (Singh, G.P., et al. 2016) which is also a compensatory mechanism in conserving oxygen (Espersen, K., et al. 2002). Blood shifts is as a result of continued peripheral vasoconstriction which causes blood to move from hypoxia-tolerant tissues e.g. muscle tissues to the hypoxia intolerant tissues e.g. brain and heart tissues as a survival mechanism (Michael Panneton, W. 2013), in the long run the tolerant tissues begin to fold under the pressure of lack of oxygen because of the high concentration of lactic acid in the cells which leads to muscle pull. This experiment as with all experiments has limitations that may have affected the outcome of the results one of such is the temperature of the room the experiment is being carried out in, because it was observed that some participants thought the warm water to be cold due to the temperature of their bodies as a result of the environment. The participants may have hyperventilated before facial immersion and could have different degrees of inhalation before the experiment (Ansay, M. et al. 2016). In conclusion, the comparison of the cardiovascular responses measured proved that wetness is the key stimuli of the diving reflex but the temperature of the water, as well as breath holding, contribute to the overall diving reflex. Holding breath did not fully trigger the diving reflex and the temperature of the water is not necessary for triggering the diving reflex. Further research needs to be done on the neurological pathways involved in the diving reflex to find physiological solutions for extending and maintain the reflex as it is an important survival mechanism. REFRENCES Ansay, M., Siliwicki, K., Kohlnhofer, B., & Castillo, S. (2016). Examining the Triggers of the Diving Reflex in Human Subjects.,. Retrieved from http://aquatic-human-ancestor.org/files/diving-reflex-triggers-humans.pdf. (On 28/12/2017) Ash, S. (2015). Infants are Natural Apeanists. Underwater Camera. , retrieved from http://www.freedive-earth.com/blog/mammalian-diving-reflex. Michael Panneton, W. (2013). The Mammalian Diving Response: An Enigmatic Reflex to Preserve Life? Physiology, 28(5), 284–297. http://doi.org/10.1152/physiol.00020.2013 (26/12/2107) Brown, C. M., Sanya, E. O., & Hilz, M. J. (2003). Effect of cold face stimulation on cerebral blood flow in humans. Brain Research Bulletin, 61(1), 81-86. doi:10.1016/S0361-9230(03)00065-0 Dampney, R. A. L. (2016). Central neural control of the cardiovascular system: Current perspectives. Advances in Physiology Education, 40(3), 283-296. doi:10.1152/advan.00027.2016 Espersen, K., Frandsen, H., Lorentzen, T., Kanstrup, I., & Christensen, N. J. (2002). The human spleen as an erythrocyte reservoir in diving-related interventions. Journal of Applied Physiology, 92(5), 2071-2079. doi:10.1152/japplphysiol.00055.2001 Foster, G. E., & Sheel, A. W. (2005). The human diving response, its function, and its control. Scandinavian Journal of Medicine & Science in Sports, 15(1), 3-12. doi:10.1111/j.1600-0838.2005. 00440.x Gooden, B. A. (1994). 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