The immediate decrease in all cardiovascular parameters in our patients can be explained by changes in the autonomic balance as it has been previously reported that sympathetic activity is lower during left nostril breathing.[5
] It has also been reported that exclusive left nostril breathing, repeated 4 times a day for a month reduced sympathetic activity.[7
We have earlier reported that the practice of sukha pranayama for 5 min at a rate of 6 BPM reduces HR and BP in patients of hypertension.[9
] In both that study as well as the present study we have found significant reduction in SP values that were on the higher side despite regular medication. However we have found in both studies that DP didn’t change much and this may be attributed to the fact it was already stabilized within the normal range with medication.
The cardiovascular effects in the present study as well as our previous one are more pronounced with regard to the RPP and Do P due to the cumulative benefits occurring as a result of reduction in HR as well as BP. RPP and Do P are especially important in patient care as they are indirect indicators of myocardial oxygen consumption and load on the heart, thereby signifying a lowering of strain on the heart.[10
] The RPP also provides a simple measure of overall heart rate variability (HRV) in hypertensive patients and is a surrogate marker in situations
where HRV analysis is not available.[11
] Hence, the reduction in RPP in our study implies better autonomic regulation of the heart in hypertensive patients. A previous study from our laboratories reported that pranayama training of three months duration modulates ventricular performance by increasing parasympathetic activity and simultaneously decreasing sympathetic activity.[12
] This may explain significant decreases in HR and BP observed in the present study with pronounced effects on the heart.
Our findings are in agreement with those of a previous report that left UFNB at the rate of 6 BPM lowers HR with compensatory increase in stroke volume and end diastolic volume.[4
] Another study done on normal volunteers reported a significant decrease in SP and MP following 30 min of exclusive left nostril breathing while the small reduction in DP in that study also missed significance as in ours.[6
] This shows that similar beneficial effects can be obtained in hypertensive patients even after less than 5 min of pranayama practice. Interestingly Raghuraj and Telles reported a significant increase in HR whereas we have found a significant decrease in HR in the present study. They suggested that the fall in SP may have been influenced by changes in cardiac output (CO), peripheral vascular resistance and humoral factors.[6
] However the rise in HR in their study doesn’t support the contention of changes in CO and if there was change in peripheral vascular resistance, it should have been reflected in the DP changes. As the HR reduced significantly in our study, it is more plausible that the fall is SP is related to CO. They had not used timed breathing rates in their study whereas our subjects were breathing at the rate of 6 BPM and this may have harmonized respiratory and cardiovascular Meyer rhythms, resulting in changes in HR as well as BP. Breathing at the rate of 6 BPM increases vagal modulation of sinoatrial (SA) and atrioventricular (AV) nodes[13
] and enhances baroreceptor sensitivity[14
] by entraining all RR interval fluctuations, thereby causing them to merge at the rate of respiration and to increase greatly in amplitude. This increase in RR interval fluctuations enhances baroreflex efficiency and may have contributed towards lowering the BP.[15
] Increase vagal modulation of SA and AV nodes along with enhancement of baroreceptor sensitivity may be responsible for reduction in HR and subsequent fall in SP evidenced in our study.
Interestingly the gender based sub-analysis of our data reveals that our male participants evidenced significant reductions in HR and SP with an insignificant decrease in DP while in female participants only the HR decreased significantly with an insignificant decrease in SP. The statistically insignificant increase in DP in our female participants as opposed to its decrease in our male participants seems to have influenced the overall result with regard to DP. Similar differences between genders following UFNB have been reported suggesting that there may be a nostril laterality affecting the autonomous nervous system differentially in males and females.[16
] The differential effect on BP between genders as evidenced by our study is in agreement with another previous study in normal healthy volunteers that reported significant reduction in HR, SP and DP after 15min of left nostril breathing in males while the reduction in females was significant only with regard to HR.[17
] The different response of our female participants may also be due to the fact that most of them were peri and postmenopausal and this may have influenced their autonomic status.
It is concluded that CNP is effective in reducing HR and SP in hypertensive patients on regular standard medical management. To the best of our knowledge, there is no previous published report on immediate effects of left UFNB in patients of HT and ours is the first to report on this beneficial clinical effect. This may be due to a normalization of autonomic cardiovascular rhythms with increased vagal modulation and/or decreased sympathetic activity along with improvement in baroreflex sensitivity. Further studies are required to enable a deeper understanding of the mechanisms involved as well as determine how long such a BP lowering effect persists. We recommend that this simple and cost effective technique be added to the regular management protocol of HT and utilized when immediate reduction of BP is required in day-to-day as well as clinical situations.