EFFECT OF REBREATHING ON RESPIRATORY RATE & EFFECT OF BREATHING ON HEART RATE
Learning objectives
By the end of today's Experiments you will be able to describe and explain the:
– Effects on the respiratory pattern of rebreathing expired gas
– Relationship between breathing and heart rate
Exercise 1
• In this exercise, you will observe the effect of rebreathing exhaled gases.
Theory
• When a person breathes in a bag concentration of oxygen decreases and that of carbondioxide increases
• This stimulates the respiratory centre and person starts breathing rapidly and deeply(hyperventilate) to bring back the comcentrations to normal
Requirements
• A volunteer
• Power lab setup for breathing experiment
• Respiratory belt
• Paper bag
Procedure
• You will need to obtain a medium-sized paper bag. When re-breathing, the volunteer should place this so that it covers the nose and mouth and forms a tight seal.
Procedure
• Click Start. Enter a comment: 'baseline', and click Add.
• Record the baseline for 2-3 minutes.
• Enter a comment: 'rebreathing'.
• Click Add and immediately ask the volunteer to place the paper bag over the nose and mouth, and rebreathe the air in the bag.
• Enter a comment: 'breathe'.
• After 60 seconds of rebreathing, click Add; then immediately ask the volunteer to remove the paper bag from the nose and mouth.
• Continue recording for 60 seconds.
• Click Stop.
Analysis
• Rebreathing from a closed bag results in arterial hypercapnia (raised partial pressure of carbon dioxide), which stimulates respiration. How was this evident in this exercise? (That is, did the depth or rate or both increase during rebreathing compared to normal breathing?)
Exercise 2
• In this exercise, you will record and examine the effect of breath-holding on heart rate.
Theory
• Respiratory sinus arrhythmia (RSA) is a naturally occurring variation in heart rate that occurs during a breathing cycle. Heart rate increases during inspiration and decreases during expiration. Heart rate is normally controlled by centers in the medulla oblongata. One of these centers, the nucleus ambiguus, increases parasympathetic nervous system input to the heart via the vagus nerve. The vagus nerve decreases heart rate by decreasing the rate of SA node firing. Upon expiration the cells in the nucleus ambiguus are activated and heart rate is slowed down. In contrast, inspiration triggers inhibitory signals to the nucleus ambiguus and consequently the vagus nerve remains unstimulated.
• On an electrocardiogram this phenomenon is seen as subtle changes in the R-R interval synchronized with respiration. The R-R interval on an ECG is shortened during inspiration and prolonged during expiration. RSA is very pronounced in children, but without sufficient cardiovascular exercise it gradually disappears in the late teens. Adults in excellent cardiovascular health, such as endurance runners, swimmers, and bicyclists, are also likely to have a pronounced RSA. Meditation and relaxed breathing techniques can temporarily induce RSA. RSA becomes less prominent with age, diabetes and cardiovascular disease.
• Previous studies have shown that the efficiency of pulmonary gas exchange is improved by RSA, suggesting that RSA may play an active physiologic role. The matched timing of alveolar ventilation and its perfusion with RSA within each respiratory cycle could save energy expenditure by suppressing unnecessary heartbeats during expiration and ineffective ventilation during the ebb of perfusion. Furthermore, evidence has accumulated of a possible dissociation between RSA and vagal control of that heart rate, suggesting differential controls between the respiratory modulation of cardiac vagal outflow and cardiac vagal tone. RSA or heart rate variability in synchrony with respiration is a biological phenomenon, which may have a positive influence on gas exchange at the level of the lung via efficient ventilation/perfusion matching
Requirements
• A volunteer
• Power lab setup for breathing experiment
• Respiratory belt
• Finger pulse transducer
Procedure
• Leave the respiratory belt fastened around the abdomen of the volunteer.
• Connect the finger pulse transducer to Input 2 on the PowerLab.
• Place the pressure pad of the finger pulse transducer against the tip of the middle finger of either hand of the volunteer. Use the Velcro strap to attach it firmly - neither loose nor tight.
• Ensure that the person sits quietly with his or her hands resting in their lap, or on a bench, to minimize transducer movements.
Procedure
• Click Start.
• Record a baseline heart rate and breathing pattern for two minutes. (Variation in the heart rate is most evident with slow, deep breathing.)
• After recording the baseline signals, enter a comment: 'inhale, hold'.
• Click Add, and immediately ask the volunteer to take a deep breath and hold it in for as long as possible.
• While the volunteer is not breathing, enter a comment: 'breathe'.
• When the volunteer begins breathing, click Add.
• Click Stop.
• The volunteer can now relax and breathe normally.
Analysis
• Heart rate variations within the breathing cycle should be seen best at a timescale compression of 20:1.