Effect of Holding Breath on Blood Flow

CARDIOVASCULAR PRACTICAL WRITE-UP

ABSTRACT

Humans exhibit a complex physiological response to various stimuli in order to survive. The Valsalva manoeuvre increases the intrathoracic pressure and reduces venous return, cardiac output and arterial pressure. Facial immersion results in bradycardia, peripheral vasoconstriction, apnoea and hypoxia. Breath holding has a similar effect to facial immersion. An ECG was recorded to measure heart rate and an infrared finger pulse transducer was used to measure peripheral blood flow. The investigation was carried out on 11 healthy adults at University of Plymouth, using LabChart software. The Valsalva manoeuvre was carried out in a seated position. The dive response was completed by the subject voluntarily submerging their face into a shallow water bath for as long as it was comfortably possible. Expected results were obtained in half of the cases. During the Valsalva manoeuvre, mean heart rate increased during the straining process, followed by a slight decrease during the release, but did not return to resting. Mean peripheral blood flow increased during the strain and decreased during the release, below the baseline. At rest, mean heart rate and peripheral blood flow were significantly higher than during the dive response. During the breath hold, mean heart rate increased above the baseline whilst mean peripheral blood flow decreased below it.

INTRODUCTION

The electrocardiogram (ECG) is widely used and extremely useful ­in contemporary medicine. ECG machines measure the rhythm and electrical activity of the heart. An ECG is crucial for the identification of disorders of cardiac rhythm, diagnosis of abnormalities of the heart, such as myocardial infarction, and a helpful clue to the presence of generalised disorders that affect the rest of the body, such as electrolyte disturbances (Houghton and Gray, 2014). An ECG reading consists of a series of waves (Figure 1). P waves are a result of atrial depolarisation, QRS complex is due to ventricular depolarisation, T waves show ventricular repolarisation, U waves are not always detected due to their small size, but these waves are thought to be due to the repolarisation of the Purkinje fibres.

Figure 1: A normal ECG reading (adapted from Virtual Medical Centre, 2006).

The Valsalva manoeuvre involves forceful expiration against a closed glottis, examples of this include straining during defaecation or during childbirth. There are four phases to the Valsalva manoeuvre (see table 1). Immersion of the face in ice-water, known as the dive response, stimulates a complex physiological response. Smith and Kampine (1990) reported that breath holding alone will produce similar results to the dive response, however deviations from the resting values will be less drastic. Breath holding creates a negative suction pressure in the thorax and inflates the organs, resulting in the heart taking longer to fill with blood and therefore creating a slower heart rate (Cheng, 2012). 

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Table 1: Summary of the responses at each phase of the Valsalva manoeuvre. Phase 1 is the onset of straining and phase 3 is the release of straining, where pulmonary blood flow begins to return to normal (Phillips and Donofrio, 2009).

Blood pressure regulation is an important part of homeostasis and is regulated by regulating cardiac output and total peripheral resistance (Vaswani et al. 2016). During a number of unfamiliar environments, which will be explored further in this investigation, the cardiovascular system adopts a ‘fight or flight’ response in order to survive. Mechanisms such as bradycardia and reduced peripheral blood flow, in order for the vital organs to benefit from maximal oxygen levels, are included in this response. Any factor causing cardiac output to increase, including increased heart rate, will elevate blood pressure and promote blood flow.

In this study, an ECG was recorded to measure heart rate and an infrared finger pulse transducer was used to measure peripheral blood flow. The objective of this study was to compare the effects of the Valsalva manoeuvre, dive response and breath holding on heart rate (HR) and peripheral blood flow (PBF) in healthy adults. HR at rest was firstly compared with HR during strain and HR during release. Resting HR was also compared to HR during dive and HR during breath hold. PBF at rest was compared with PBF during strain and PBF during release. Resting PBF was also compared to PBF during dive and PBF during breath hold.

MATERIALS AND METHODS

As per protocol.

RESULTS

Statistical values were generated for each experimental condition, including mean, standard deviation and 95% confidence interval (shown in tables 2.1-2.4). During the Valsalva manoeuvre, mean heart rate increased to 86.096 bpm during straining, followed by a slight decrease to 83.984 bpm during the release, but did not return to resting rate of 70.05 bpm. Mean peripheral blood flow increased to 5.340 mV/sec during the strain and decreased to 4.490 mV/sec during the release, below the baseline of 5.113 mV/sec. At rest, mean heart rate and peripheral blood flow were significantly higher than during the dive response. During the breath hold, mean heart rate increased above the baseline whilst mean peripheral blood flow decreased below it.

A one-way ANOVA was conducted testing for an effect on heart rate due to the Valsalva manoeuvre, dive response and breath hold*. There was no statistically significant difference between means for each experimental state as determined by the one-way ANOVA (F(2,30) = 2.24, p = 0.1239) and (F(2,30) = 1.47, p = 0.2453) respectively.

The test was repeated, testing for an effect on peripheral blood flow due to the Valsalva manoeuvre, dive response and breath hold*. There was no statistically significant difference between means for each experimental state as determined by the one-way ANOVA (F(2,27) = 0.10, p = 0.9022) and (F(2,27) = 3.13, p = 0.0600) respectively.

*N.B. Dive response and breath hold were both included in the same ANOVA test, whereas the Valsalva manoeuvre was a separate test.

The results of the one-way ANOVA (i.e. p > 0.05) indicate that there is not enough evidence to reject the null hypothesis that the means are equal under all conditions.

Table 2.1: Statistical analysis comparing resting heart rate (HR) against heart rate during the Valsalva manoeuvre.

Table 2.2: Statistical analysis comparing resting heart rate (HR) against heart rate during the dive response and breath hold.

Table 2.3: Statistical analysis comparing resting peripheral blood flow (PBF) against peripheral blood flow during the Valsalva manoeuvre.

Table 2.4: Statistical analysis comparing resting peripheral blood flow (PBF) against peripheral blood flow during the dive response and breath hold.

Experimental state of participant

Figure 2.1: Boxplot of heart rate data at rest, during Valsalva manoeuvre (strain and release), during dive response and during breath hold (n=11). X indicates mean heart rate in each state, median heart rate is indicated by a horizontal line within the box, outliers are also indicated by a circle.

State of participant

Experimental state of participant

Figure 2.2: Boxplot of peripheral blood flow data at rest, during Valsalva manoeuvre (strain and release), during dive response and during breath hold (n=10). X indicates mean peripheral blood flow in each state, median peripheral blood flow is indicated by a horizontal line within the box.

DISCUSSION

The Valsalva manoeuvre increases the intrathoracic pressure and reduces venous return, cardiac output and arterial pressure (Smith and Kampine, 1990). The dive response overrides basic homeostatic reflexes, causing apnoea, bradycardia, hypoxia and peripheral vasoconstriction. Slowing the heart rate reduces the need for oxygen in the blood, leaving more to be available to other organs. Capillaries begin to close off, stopping blood circulation to the periphery of the body, leaving more blood for use by the vital organs. Breath holding causes bradycardia by activation of the parasympathetic nervous system, in addition to decreased cardiac output and peripheral vasoconstriction. Expected results are shown in table 3. The expected trend was not followed in half of the cases, however 4/8 results obtained were expected.

Table 3: Expected results of heart rate and peripheral blood flow during each experimental state. Red cells indicate the mean results obtained did not match the expected results, green cells indicate the mean results obtained correspond to the expected results. *Increase or decrease in relation to the resting values.

Normal resting heart rate is between 60-100 bpm. Nearly all values obtained were within this interval. Although stress, anxiety and awareness of being monitored can all cause heart rate to increase. The electrodes were easy to attach to the participant with little room for error. However, the finger pulse transducer needed to be tightened onto the participant with a Velcro strap. If the infrared plethysmograph was applied too tightly or too loosely, waveforms would have been distorted and therefore analysed inaccurately. This could be checked by comparing the waveform obtained against a standard diagram of waves from a ‘properly applied’ transducer or having a trained member of staff check the transducer. Another source of error could have been due to the participant not being completely relaxed or the participant making a sudden movement whilst being monitored. Additionally, the ‘strain’ of the Valsalva manoeuvre could have been subjective. Each participant may have determined the force of the strain differently. For example, a person straining with more force would have a larger decrease in venous return, causing a larger decrease in blood pressure which will initiate a response, increasing heart rate more than a person who strains with less force. To overcome this, participants should be instructed to carry out a strain with maximal force and should be allowed to practice the process. An additional experiment could be carried out, performing the strain in different positions; standing, seated and supine. Mean peripheral blood flow increased from baseline during the strain, however the median data was below baseline as expected. A large spread of data has caused the mean value to be increased dramatically in this case.

Both systolic and diastolic blood pressure could have been measured during each of the experimental states to provide evidence of peripheral vasoconstriction (i.e. when vessels constrict, blood pressure would be expected to increase). Blood pressure is regulated by cardiac output and total peripheral resistance, therefore any factor affecting cardiac output will directly affect blood pressure and blood flow. Future studies should be carried out considering the water temperature during the dive response, as colder water is likely to decrease the heart rate further from the baseline.

CONCLUSION 

Mean heart rate increased during straining, due to the baroceptor mediated effect in response to decreased blood pressure. Mean heart rate and peripheral blood flow decreased during the dive response, allowing more oxygen to be taken up by the vital organs for survival. Peripheral blood flow also decreased during the breath hold for the same reason. Mean heart rate increased slightly from the resting value during the breath hold. Peripheral blood flow decreased and increased from baseline for the strain and release respectively, against expected results.

REFERENCES

• Cheng, R. (2012). How does holding your breath affect heart rate? Available: http://explorecuriocity.org/Explore/ArticleId/553/how-does-holding-your-breath-affect-heart-rate-553.aspx. Last accessed: 03/12/2018.
• Houghton, A. and Gray, D. (2014). Making sense of the ECG: a hands-on guide. 4^th ed. CRC Press, Florida. ISBN 978-1-4441-8183-8.
• Phillips, E.L. and Donofrio, P.D. (2009). Autonomic disorders. Encyclopedia of Neuroscience, pp. 799-808.
• Smith, J.J. and Kampine, J.P. (1990). Circulatory physiology – the essentials. 3^rd ed. Williams and Wilkins, Baltimore. ISBN 0-683-07775-9.
• Vaswani, A., Khaw, H.J., Dougherty, S., Zamvar, V. and Lang, C.C. (2016). Cardiology in a heartbeat. Scion Publishing, Banbury. ISBN 978-1-907904-78-3.
• Virtual Medical Centre. (2006). ECG/EKG (electrocardiogram). Available: https://www.myvmc.com/banners-heart-health-centre/ecg-ekg-electrocardiogram/Last accessed: 30/11/2018.