Respiratory psychophysiology in hypertension research

Clinical Applications of Breathing Regulation

Breathing training is widely used as an aid in reducing anxiety states, but several other applications also show promise. This article reviews evidence that normalizing breathing patterns may offer help in some cases of essential hypertension, angina, functional chest disorder, chronic obstructive pulmonary disease (COPD), and cardiac rehabilitation. Hyperventilation and hypo-ventilation, inhibited breathing, and breath suspension are all deviations from an optimal breathing pattern in which breathing volume is closely matched to metabolic needs. Such disordered breathing has varying effects on acid/base balance, arterial diameter, and sodium retention by the kidneys. Therefore, a chronic breathing imbalance can contribute to pathophysiology, which may be remediable to an extent by altering habitual breathing patterns.

Different breathing patterns in healthy and asthmatic children: responses to an arithmetic task

Asthma patients have been reported to be sensitive to breathlessness, independent of the degree of airway obstruction. Paying attention and task performance may induce changes in breathing pattern and these in turn may mediate such a feeling. The present experiment investigates whether strained breathing induced by an arithmetic task was different in children with asthma compared to healthy children.

METHODS

Seven healthy and eight asthmatic but symptom-free school children were equipped with electrodes for surface electromyographic (EMG) measurements of diaphragm, abdominal and intercostal (IC) muscles and with a strain gauge to monitor the pattern of breathing at rest and during an arithmetic task. The relative duration of exhalation and the relative speed of exhalation are used as measures of straining. The phase angle of maximal respiratory muscle activities relative to the maximal chest extension (MCE) are additional discriminating parameters.

RESULTS

Asthmatic children breathed more slowly and already at rest the phase of their respiratory muscle activity appears to be different. While in healthy children the maximal activity of the (left)abdominal muscles occurred 5+/-29% later than the MCE, in children with asthma the maximal activity occurred 26+/-30% of the cycle earlier than MCE. In children with asthma the activity of the IC muscles starts weaning already at 10+/-30% before MCE, in contrast to the healthy children in which intercostal muscle weaning starts only at 1+/-24% after MCE. During arithmetic, the significant difference between the groups in this respect disappeared.

CONCLUSION

Children with asthma show, even at rest, signs of respiratory muscle straining, probably in order to keep close control over the airflow in a similar way as healthy children during mental tasks. Such a 'careful' breathing pattern may work to prevent airway irritation also when they are free of symptoms.

Resting end-tidal CO2 and negative affectivity

OBJECTIVE

Dhokalia, Parsons, and Anderson (Psychosom Med 1998;60:33-37) found a positive correlation between a trait measure of negative affectivity (NA; neuroticism) and resting end-tidal fractional concentration of CO2 (FetCO2) (fractional-concentration of end-tidal carbon dioxide) in a nonclinical sample. This contrasts sharply with studies reporting a negative association of FetCO2 with state measures of NA and with studies reporting no or a negative relationship between FetCO2 and trait NA. In two studies we aimed to clarify this paradox.

MATERIALS AND METHODS

In the first study, 110 participants (83 women) completed the PANAS and a Checklist for Psychosomatic Symptoms in daily life. FetCO2 was measured noninvasively during 5 minutes via a nose cannula connected to a capnograph. In the second study, FetCO2 of high (N= 20, 10 men) and low (N= 20, 10 men) NA participants was sampled once with a nasal cannula and once while breathing through a mouthpiece for 6 minutes each during rest, completion of the NEO-PI-R questionnaire, and completion of a verbal knowledge test.

RESULTS

The first study found no association between trait NA and resting FetCO2 after partialling out the effects of gender, menstrual phase, and use of oral contraceptives. The second study showed that FetCO2 increased significantly in the high NA group only when the particpants filled out the questionnaires, regardless of its type.

CONCLUSIONS

Overall, no association between dispositional NA and cross-situational FetCO2 was observed. Apparently inconsistent findings may be caused by lack of control for hormonal status and mental load during testing.

Determining the relationship of heart rate and blood pressure using voluntary cardio-respiratory synchronization (VCRS)

Voluntary cardio-respiratory synchronization (VCRS) was used to investigate heart rate and blood pressure changes in the supine position in 21 subjects. VCRS involves a breathing pattern that is synchronized with the cardiac cycle. The signals to inhale and exhale are derived from the ECG. In this study, the subjects inspired for four heart beats and expired for four heart beats for 35 cycles. This technique is designed to have the heart beat occur at exactly the same phase in the respiratory cycle and lends itself to the study of the influence of the respiration cycle on heart rate and blood pressure changes. The heart rate and blood pressure changed simultaneously in the same direction, with the largest significant positive change occurring on the second heart beat during inspiration. The authors discuss the potential of VCRS for research, and clinical applications as a respiration modulator for hypertension therapy or increased heart rate variability.