Ash, S. (2015).DIVINGREFLEX PRACTICALWORDCOUNT:2000ANNIEOMOREGIE (U1674367) | PHYSIOLOGY: CONTROL AND COORDINATION | 14/12/2017INTRODUCTIONDivingreflex is a physiological mechanism that allows animals including humans toremain submerged in water and it comprises of three independent reflexes thatcause physiological changes that counter homeostatic control (MichaelPanneton, W. 2013) and they are bradycardia which is the slowing down of theheart rate, peripheral vasoconstriction, and hypertension. It is a verypowerful collection of reflexes that allow the preservation of oxygen foraerobic 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 theycan 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 ofsurvival, this is the main physiological purpose of the diving reflex.
Thelevel at which humans use this reflex is limited in terms of time compared tothe aquatic and marine mammals as they can’t remain submerged for long periodsof time. The aim of the diving reflex practical is to assess the cardiovascularchanges in heart rate and mean arterial pressure during simulated diving indifferent conditions to identify the key stimuli for the diving reflex. It wastherefore hypothesized that facial immersion in water will lead to a decreasein heart rate and an increase in mean arterial pressure, if so what effect doesthe temperature of the water have on the extent of the diving reflex in humans.METHODPARTICIPANTSTwentyhealthy participants in groups of two, aged 19-25 years took part in theexperiment voluntarily after signing a consent form which was in line with theHealth and Safety guidelines of the School of Applied Sciences, University ofHuddersfield.ExperimentalProcedureHeartrate, systolic and diastolic pressure were measured using a blood pressure (BP)monitor during each of the conditions.
The cuff of the monitor was positionedon the right arm at the same level as the heart for each participant and theparticipants were seated comfortably upright and breathing normally before therest reading was taken twice to ensure a steady heart rate and blood pressureat the start of the investigation. The first condition required theparticipants to hold their breath in air until a BP/HR reading is obtained, thesecond condition required the participants to submerge their faces in warmwater at 25?c after a 5 minutes’ rest to allow the participant’s cardiovascularvalues return to a steady baseline. Their faces are kept submerged until areading is obtained.
The same procedure is carried out in the third conditionexcept that the temperature of the water is 10?c. A bowl, towel, thermometerand tap water were required for the experiment.DataAnalysisDataanalysis was carried out using the Statistical Package for the Social Sciences(SPSS). Normality tests and descriptive analysis which included the measures ofcentral tendency and variability were used to describe the results of the fourconditions the participants were subjected to. To test the hypothesis, therepeated measures ANOVA test was used to compare and test the differencesbetween the results of the conditions. The same participants were used throughoutthe experiment and the conditions and results are related also the data fit theassumptions necessary to run the repeated measures ANOVA (LaerdStatistics. Lund Research Ltd. 2013).
The Mauchly’s test of Sphericity was used to test forunequal variances between all the combinations of the conditions as a violationof this would make the repeated measures ANOVA to become too flexible (LaerdStatistics. Lund Research Ltd. 2013).RESULTSResults from the normality test and graphical representation of thefrequency distribution of the heart rate and mean arterial pressure during eachcondition suggested that the data was parametric because the data samples were<50 the Shapiro-Wilk tests of normality was considered and the significancein each case was greater than 0.05.
For the sake of clarity, the two cardiovascularresponses will be evaluated separately.HEART RATEThe table and graph below show the results of the descriptive analysisof 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 facialimmersion in water and decreases further in cold water but we cannot concludebased on the graph hence to test if the difference shown on the graph issignificant. The Mauchly’stest of Sphericity gave a significance of 0.
72 p<0.05 hence the data did notviolate sphericity. A repeated measures ANOVA with no correction resolved thatthe mean heart rate is statistically different (F (3,24) =7.465, p<0.05. Todetermine where the differences occurred a Bonferroni post hoc test resulted ina pairwise comparisons table (appendix) which revealed that holding one'sbreath which reduced heart rate was not statistical different on the heart rate whenat rest, in cold water and warm water conditions (p=0.363,p=1.
0 and p=1.0respectively) also the difference between the mean heart rates in warm and coldwater conditions had a statistically significant difference from rest (p=0.016and p=0.
001 respectively). There were no statistically significant differencesbetween the effect of warm and cold water had on heart rate p=0.928.MEANARTERIAL PRESSURE (MAP)Themean arterial pressure was calculated from the systolic and diastolic pressuresrecorded with the formula MAP=(SBP+2DBP/3). The table and graph below summarizethe 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 withfacial immersion in water also the pressure is higher in cold water than inwarm. The data did not violate the assumption of sphericity 0.92 p<0.
05 andthe repeated measures ANOVA showed that the data the difference isstatistically significant (F (3,24) =12.046) p<0.05. the post hoc testproves that the mean arterial pressure measured in cold water conditions has asignificant 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 notexhibit any significant statistical difference from the MAP at rest.
DISCUSSION/CONCLUSION The results show a difference between the heart rate and mean arterialpressure during rest and apnea (holding breath) but the test suggests that thedifference is not statistically significant. Although this may be the case ofthis experiment previous experiments concluded that apnea is necessary to thediving 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 maybecause the participant is consciously preventing oxygen uptake which pushesthe body to conserve oxygen, the chemoreceptors are stimulated by the risingCO2 levels in the bloodstream causing the sympathetic nervous system tostimulate vasoconstriction and the parasympathetic system to decrease the heartrate (Dampney,R.
A. L. 2016).Compared to holding breath the changes in the cardiovascular outputsduring facial immersion is statistically significant because direct facialcontact with water stimulates the diving reflex (Foster, G. E., & Sheel, A. W.
2005). Facial immersion in waterstimulates both the thermoreceptors and mechanoreceptors to detect moisture (ColumbiaChronicle. 2014). These receptors relay the message to the brain via theparasympathetic vagus nerve where the respiratory center stimulates a reflexapnea and bradycardia (Michael Panneton, W. 2013), while the trigeminal nerveactivates the sympathetic nervous system to cause peripheral vasoconstrictionwhich increases the blood pressure. The temperature of the water also has arole to play in accentuating the diving reflex as the results reveal that thedifference between the decrease heart rate and increase in mean arterialpressure compared to warm water is significant but it is not a stimuli for thediving reflex because a localized cold stimulus to the face increases meanarterial pressure via the trigeminal nerve hence it only represents a fractionof 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 whichtriggers the activity of the sympathetic nervous system to cause skin vasoconstrictionand hair rising to increase skin insulation and the release of norepinephrineand epinephrine which leads to peripheral vasoconstriction of the blood vesselsand increased blood pressure.
the reverse is for warm water which is detectedby the warmth receptors on the face causes vasodilation of the blood vesselsand reduced blood pressure (Dampney, R. A. L. 2016). The diving reflex appliesthe spinothalamic pathway because it employs the use of different receptors(thermoreceptors and mechanoreceptors) to elicit, pressure and temperaturesensations (Greenhough, K. 2017) that are transmitted via the trigeminal nerveto the thalamus for central processing and finally the response is relayedthrough the vagus nerve which innervates the heart to carry out the parametersmeasured in the experiment. (Singh, G.P.
& Chowdhury, T. 2017)Thediving reflex shares similarities with the trigeminal-cardiac reflex which itis a subtype of, but what differs between the two is the effect on bloodpressure. While the trigeminal-cardiac reflex causes blood pressure to increasethe diving reflex does the opposite. This is due to the sympathetic stimulationduring diving (Singh, G.P.
, et al.2016) caused by the rising CO2 levels in the blood when holding breath. Thiseffects on the heart are carried out by the beta-adrenoreceptors and muscarinicreceptors (Klabunde, R.E. 2016).Furtherchanges that can occur as a result of the maximal diving reflex are the contractionof the spleen and blood shift. Splenic contraction releases more red bloodcells hence increasing the hemoglobin content in circulation (Singh, G.P.
, et al. 2016) which is also acompensatory mechanism in conserving oxygen (Espersen, K., et al. 2002).
Blood shifts is as a result of continued peripheralvasoconstriction which causes blood to move from hypoxia-tolerant tissues e.g.muscle tissues to the hypoxia intolerant tissues e.g. brain and heart tissuesas a survival mechanism (Michael Panneton, W. 2013), in the long run the toleranttissues begin to fold under the pressure of lack of oxygen because of the highconcentration of lactic acid in the cells which leads to muscle pull.
Thisexperiment as with all experiments has limitations that may have affected theoutcome of the results one of such is the temperature of the room theexperiment is being carried out in, because it was observed that someparticipants thought the warm water to be cold due to the temperature of theirbodies as a result of the environment. The participants may havehyperventilated before facial immersion and could have different degrees ofinhalation before the experiment (Ansay, M. etal. 2016).Inconclusion, the comparison of the cardiovascular responses measured proved thatwetness is the key stimuli of the diving reflex but the temperature of thewater, as well as breath holding, contribute to the overall diving reflex.Holding breath did not fully trigger the diving reflex and the temperature ofthe water is not necessary for triggering the diving reflex.
Further researchneeds to be done on the neurological pathways involved in the diving reflex tofind physiological solutions for extending and maintain the reflex as it is animportant survival mechanism. REFRENCES Ansay, M., Siliwicki,K., Kohlnhofer, B., & Castillo, S.
(2016). Examining the Triggers of theDiving 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 NaturalApeanists. Underwater Camera. , retrieved fromhttp://www.
freedive-earth.com/blog/mammalian-diving-reflex.Michael Panneton, W.(2013). The Mammalian Diving Response: An Enigmatic Reflex to PreserveLife? 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 cerebralblood flow in humans. Brain Research Bulletin, 61(1), 81-86.doi:10.1016/S0361-9230(03)00065-0Dampney, R. A. L.
(2016). Central neural control of the cardiovascular system: Currentperspectives. Advances in Physiology Education, 40(3), 283-296.
,Frandsen, H., Lorentzen, T., Kanstrup, I., & Christensen, N.
J. (2002). Thehuman spleen as an erythrocyte reservoir in diving-related interventions. Journalof Applied Physiology, 92(5), 2071-2079. doi:10.1152/japplphysiol.
00055.2001Foster, 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.
xGooden, B. A. (1994).
Mechanism of the human diving response. Integrative Physiological andBehavioral Science: The Official Journal of the Pavlovian Society, 29(1),6-16. doi:10.1007/BF02691277Greenhough, K.(2017). Sensation and Sensory Processing. MicrosoftPowerPoint.
Retrieved from trigeminal brain stem cardiovagal and sympatheticpathwaysHempleman, H. V.,& Lockwood, A.
P. M. (1978).
The physiology of diving in man andother animals. London: Edward Arnold.Klabunde, R.E.
(2016). Cardiovascular Physiology Concepts. Retrieved from http://www.cvphysiology.com/Blood%20Pressure/BP008. (17/1/2018)Panneton, W. M.
, Gan,Q., & Juric, R. (2010). The rat: A laboratory model for studies of thediving response. Journal of Applied Physiology, 108(4),811-820.
(2014). Tactile fluidity: The Human sense of wetness likelya collaboration of receptors. Retrieved from http://www.
columbiachronicle.com/health_and_tech/article_080f610a-5114-11e4-9d76-0017a43b2370.html. (On 4/1/2018)Singh, G.P.,Chowdhury, T., Bindu, B., & Schaller, B.
(2016). The Trigeminal-Cardiacreflex: Beyond the Diving Reflex. frontiers in Neurology and Frontiers inNeuroscience, 7 (221), 18-23. doi:doi:101.
3389/fneur.2016.0021.Singh, G.P. &Chowdhury, T. (2017).
Trigeminocardiac reflex pathway. drawing. Journalof Neuroanaesthesiology and Critical Care., (73). India: Wolters Kluwer.