Nitric Oxide (NO) is a remarkably simple component which has received a great deal of attention for its versatility and importance as a key intracellular and intercellular signaling molecule. It is endogenously generated in mammalian cells and regulates a range of physiological and pathophysiological mechanisms. Previously, it was considered as an atmospheric pollutant with no biological role. However, it was demonstrated independently by Ignarro et al., and Palmer et al.,
NO is involved in several regulatory, protective, and defensive processes and is also secreted in response to inflammatory processes. It acts as a powerful vasodilator that relaxes the smooth muscle fibers of the vascular wall. It regulates blood vessel tone; it functions as a biological mediator comparable to neurotransmitters in the neural system. It acts as an important host defense in the immune system and also acts as a cytotoxic agent in the pathological process, particularly in inflammatory diseases. NO is produced by various cells throughout the body including the respiratory airways. Recent pathbreaking research by Weitzberg and Lundberg demonstrated that nasal Nitric Oxide levels in the airways increase considerably during humming compared to quiet nasal exhalation
This review is about understanding the application of humming in the expression of NO in the airways and its role in regulation of various functions in the respiratory system. We review certain experiments made on the basis of acoustic background of humming that enhance the NO expression in the paranasal sinuses. We also make an effort to evaluate the suitability of BhPr for its ability to enhance the NO expression in the paranasal sinuses. According to the ancient yoga text Hatha Yoga Pradeepika, BhPr is producing a humming sound, at a sustained low pitch, depicting a female bumblebee. Adding the dimension of acoustics to breathing in BhPr, make it unique among other pranayamas. The humming sound is produced during exhalation after a controlled inhalation. This variation of BhPr is done as a prelude to classical version of BhPr. Occlusion of the external ear canals during humming with shanmukhi mudra, another unique feature of BhPr enhances the effect of humming. Research on this variation of BhPr has been growing expeditiously. The acoustics and its overt features can be observed and measured in laboratory conditions which is not common in yoga studies. From various studies done till now it is evident that BhPr influences multiple systems in the body inclusive of the respiratory system. Expression of NO and its role as a therapeutic tool for regulation of respiratory system has been implicated in some BhPr studies that is discussed later in this review.
The classical version of BhPr as in the ancient text, Hatha Yoga Pradipika, includes humming during inhalation also, producing a reverberating sound in high pitch depicting a male bee along with humming during exhalation in a sustained low pitch depicting a female bumble bee. Breathing a physiological process, completes a respiratory cycle with both inhalation and exhalation. It can be observed that the dimension of the acoustics differs from humming during exhalation to humming during inhalation. Experiments made till now have expounded the techniques and efficacy of humming during exhalation and suggest that there is an enhanced expression of NO in the upper respiratory airways
In this review we have made an effort to understand the experiments related to the acoustics of humming in enhancing the expression of NO in the paranasal sinuses. It is done with a brief description of NO in general and role of NO in the respiratory airways in particular. A comparison of humming and preliminary version of BhPr is made with the help of yoga texts, scientific literature pertaining to acoustics of humming with reference to literature pertaing to the voice production. A trail is made to evaluate the suitability of BhPr with specific reference to the acoustics in this context. We also examine relevant literature pertaining to the classical version of BhPr which emphasizes on the acoustics of humming both during inhalation and exhalation according to the yoga texts and experiments in the literature pertaining to voice production. We hypothesize that the classical version of BhPr may be a wholesome approach towards enhanced stimulation of NO and provide its effective delivery, to the lower airways thereby help in its maintenance.
NO is a colorless, odourless, hydrophobic, gaseous molecule that has been recognized as an extremely important molecule in biophysics. It has a half-life of 3-5 seconds that diffuses easily through cell membranes. It is a free radical characterized by the presence of an unpaired electron and reacts with several biological compounds which explain its diverse biological effects. NO is produced by various cells throughout the body. It is synthesized by specific enzymes, semi-essential amino acid L-arginine, molecular oxygen, and various Nitric Oxide synthase (NOS) enzymes. The synthase NO has two forms: a constitutive form and an inducible form. The endothelial NOS (eNOS, NOS-I) and neuronal NOS (nNOS, NOS-III), are the two constitutive forms of NO. These eNOS and nNOS are calcium-calmodulin dependent and are activated rapidly and transiently in response to a calcium signal. They are produced in small amounts and provide a rapid pulse-like signal. The functions of endothelial NOS and neuronal NOS are regulated by two distinct types of constitutive NO synthases that have been fully characterized and are widely distributed in the body.
The expression of NO (eNOS) in the endothelial cells is the most important vasodilator mechanism responsible for the maintenance of proper vasomotor function. It is expressed by endothelial cell lining in response to agonists or shear stress. Its physiological role ranges from many other cells and tissue functions, especially in the respiratory, nervous, and immune systems. It promotes the proliferation of smooth muscle cells, platelet aggregation, white blood cell adhesion, and inflammation thereby initiating and aggravating the vascular disease. In patients exposed to vascular risk factors, impaired endothelium-dependent relaxations caused by aging, smoking, diabetes, hypercholesterolemia, hypertension, and sedentary lifestyle are detectable even before any morphological changes could be perceived in the blood vessel wall.
NO (nNOS) is readily expressed through the central nervous system. It has a role in the neural control of cerebral circulation. nNOS is also expressed in peripheral autonomic nerves which modulate blood vessel tone. When over expressed, NO is neurotoxic, and while dysfunctional nNOS signalling has been implicated in cerebrovascular disease states such as ischemia, and migraine, as well as neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease. In cerebral circulation, maintenance of endothelial NO is a crucial strategy in the prevention of cerebrovascular disease and stroke. Endothelial dysfunction in the cerebral circulation may contribute to neurologic diseases.
A third isoform, inducible NOS (iNOS, NOS-II) is not expressed in resting cells but is expressed under pathological conditions as an immune response mediator in white blood cells, epithelial cells, and other cells in response to proinflammatory cytokines. This isoform of NOS is calcium-calmodulin independent, and NO synthesis is transcriptionally controlled and steroid-sensitive. Once the enzyme is activated, it will produce large amounts of NO for a prolonged period and in high concentrations. NO (iNOS) and its reaction products are cytotoxic to viruses, bacteria, tumour cells, and at the same time possibly to host cells too. Whether the upregulated iNOS during inflammation is beneficial or harmful to the host has been debated. Inhibiting iNOS may be considered in the treatment of inflammatory diseases
In 1991, NO was detected in exhaled breath in the human breath analysis. The exhaled NO levels exhibited increased levels in asthmatic patients. These observations prompted further research on NO in the respiratory system. Upper airways were found to be the main origin of respiratory NO in healthy adults. This review pertains to NOS in the respiratory airways and its role in the respiratory system. NO concentration in the lower airways is reported to be 20 times lower than in the upper airways in normal subjects.
The para sinuses in the upper airways were found to be the main production site of NO synthesis. It yields very high concentrations, (3000-25000 ppb) with an only minor contribution from the lower airways and oral cavity in healthy subjects. Interestingly, all three isoforms of NOS are available in the upper respiratory tract. eNOS and nNOS are expressed in parasympathetic neurons innervating nasal vessels, endothelial cells, and ciliated epithelial cells. The NOS found in the paranasal sinuses is predominantly calcium-independent, a characteristic usually attributed to the NOS-II, but studies showed that it is constitutively expressed and not inhibited by steroids, the latter being typical features of constitutive NOS. Interestingly, the high expression of NOS-II was found in healthy sinus epithelium. NO, a calcium-independent inducible NOS was found in the epithelial cells lining the sinuses of healthy subjects. Strong NOS immunoreactivity was found apically in those cells in the range of 25 ppm, the highest permissible atmospheric pollution levels for NO. It was surprising at that time to find NOS-II in healthy tissue as it was believed till then that this enzyme was only expressed in inflamed tissues or activated in white blood cells. This form of NOS is produced continuously in large quantities in the normal sinus epithelial cells, as indicated by the presence of this gas in nasally derived air. NO has been involved in several functions in both the upper and lower airways. NO maintains the physiological homeostasis and regulates the airway inflammation through the expression of three NOS isoforms. NO may also regulate the nasal airway resistance to airflow (NAR). It also seems to humidify and warm the inhaled nasal airflow
From the immuno-histochemical studies, it is noted that iNOS is constantly expressed apically in the paranasal sinus epithelium. This is the enzyme that is used by the white blood cells to produce NO in defense of invasion of viruses, bacteria, or fungi and helps to keep the sinuses sterile. NO could also act as a defense mechanism in the upper airways by modulating the ciliary motility and low levels of NO can be linked to weakened mucociliary activity
Research over the past few years has shown that NO produced in the paranasal sinuses has a dual function. The high local concentration of NO in the sinuses may act as host defense and contribute to maintaining the sterility of the nasal cavities
Studies by Maniscalco et al. reported that basal NO levels in healthy subjects increase significantly during humming compared to silent exhalation. The paranasal sinuses, notably the maxillary sinus, are an important source of NO. Their research revealed that humming increases NO output 15 folds more than quiet exhalation
It is also to be noted that research carried out till now pertains to humming during the exhalation phase of breathing or exhalation phonation. It has been demonstrated that the techniques of exhalation phonation may enhance the expression of NO.
Humming has been part of the ancient technique of yogic breathing,
Occluding the external ear canal with middle fingers or by applying shanmukhi mudra is another important feature of BhPr. This mudra is carried out using all the fingers; thumbs of both hands to occlude the two ear canals, forefingers to place on the closed upper eyelids, the middle fingers on the nasal bridge to perceive the facial vibration and to partially block and regulate the passage of the breath and lastly, the ring, and the little fingers to be placed on the upper and lower lips
According to the classical variation in the ancient text, Hatha Yoga Pradipika, BhPr is performed by humming during both inhalation and exhalation; a quick inhalation, making a reverberating sound like a male black bee, and slow exhalation while softly making the sound of a female black bee in a low pitch along with shanmukhi mudra. It is also classified as one of the ashtha kumbhakas (eight pranayamas with breath retention). It is classified as a kumbhaka, as breath retention between inhalation and exhalation is performed.
Literature about speech/voice production has termed humming during exhalation as exhalation phonation and humming during inhalation as inhalation phonation. Both types of humming are used for therapeutic purposes in voice production. During phonation, the vocal folds come sufficiently close, which increases trans-glottal pressure causing the vocal folds to vibrate thereby creating a modulated airflow. It is also observed that the vibratory cycle of the vocal folds during inhalation phonation is a reversal of exhalation phonation. During exhalation phonation, breath flows upwards from the lungs and moves towards the nasal and oral cavities. During inhalation phonation, breath flows towards the lungs from the upper airway. Literature about voice production report that the natural pitch of humming during inhalation is higher than the humming during exhalation due to the lengthening and thinning of vocal folds. The acoustic component of humming during inhalation is said to be less sonorous and harsher sounding and has lesser clarity than the exhalation humming. Manipulation of the sinus and/or oral/ pharyngeal cavities during inhalation phonation increases resonance than during the exhalation phonation
It is also postulated that nasal Nitric Oxide output is considerably greater during inhalation than exhalation in healthy adults
The above information seems to support that the features of classical BhPr during inhalation may aid in better utilization of NO in the airways of the respiratory system. But to the best of our knowledge, research pertaining to humming during inhalation in the context of NO is yet to be done. Experiments with alternate exhalation humming and inhalation humming are also essential. As the exhalation part of BhPr is very encouraging, the corresponding inhalation part may also yield a similar outcome and aid in the better utility of NO to enhance health benefits.
Humming is an exceptional mechanism when volitionally performed in a certain way as reported by various studies, can stimulate a many-fold increase in NO production than during quiet exhalation. Humming enhances the NO concentrations in the para sinuses from the range of up to 20 ppm to the range of 200 ppm or more which is known to serve as anti-fungal also. Higher concentration of NO aids in better maintenance of para sinuses, which is critical to supply continuous NO to the lower airways of the respiratory system. The increased level of NO seems to be useful to treat nasal ailments such as chronic rhinosinusitis (CRS) caused by immune disorder by fungi. However, the role of an excessive amount of NO produced in inflammation which remains elusive is to be carefully examined in this context.
A case reported by Eby, George A. of a subject with chronic rhinosinusitis treated with antirhinoviral, antiherpetic, and oral antibiotics and oral decongestants was ineffective. He was administered humming at a low pitch, 60-120 times in four sessions per day for four days. As a result, all rhinosinusitis symptoms were essentially eliminated within four days
Nitric Oxide is an important biomarker in exhaled breath, as it is investigated in various pulmonary and non-pulmonary diseases. Measurement of NO in exhaled breath is used as a clinical tool to measure airway inflammatory diseases including asthma. The nasal NO was observed to be lower in aliments such as primary ciliary dyskinesia (PCD) and cystic fibrosis (CF) due to obstruction of the paranasal sinuses. In these ailments measuring exhaled NO during humming is recommended as it increases the sensitivity of the blocked condition of the ostiomeatal complex
Scientific research on acoustics of humming in the context of expression of NO in the para sinuses has made it possible to understand the efficacy of this technique to a great extent. It is also observed that the existing anatomy of the para nasals, maxillary sinuses, in particular, operate as Helmholtz resonators. These structures would resonate, when hummed at the fundamental frequency of voice at constant pressure, , due to which production of NO would be at peak level. Typically, humming per se does not define the pitch or the consistency of the pitch that is to be maintained. However, BhPr specifically indicates the pitch of the humming, and the consistency of the pitch to be maintained. These specifications seem to match with the observations made in the experiments of humming during exhalation that have proven to produce the highest level of NO. Based on these observations we argue that BhPr could be a better option in comparison to humming to efficient increase of expression of NO in the paranasal sinuses.
Another limitation of humming is that, it does not seem to provide for efficient delivery of additional NO released by humming to the lower airways. It is postulated that the prime purpose of expression of NO in the para nasals sinuses is to provide NO through auto inhalation to regulate pulmonary functions. It is also suggested that due to short lifetime of a few seconds to NO and diffusion distance, increased endogenous NO supply at low-dosage may be necessary to improve pulmonary effect in the lungs
In recent clinical trials, to overcome the depletion of physiological inhaled endogenous NO and treat consequent ailments, exogenous NO is resorted to. The exogenous NO is administered via mechanical drug delivery systems, many systems with include acoustics, are used extensively. This Inhaled Nitric Oxide is utilized to manage pulmonary arterial hypertension and ventilation-perfusion mismatch associated with cardiac pulmonary ailments. However extensive use of inhaled exogenous NO is limited by logistical and financial barriers. Observations made in the experiments of acoustics of humming during exhalation may help in understanding better management of drug delivery system.
We hypothesize that humming during inhalation may supply optimal quantity of NO to the upper and lower airways of the respiratory system. Humming during inhalation may efficiently supply NO to the sinuses to treat upper airway diseases. Regular practice of BhPr may help to strengthen the respiratory system and can be a preventive measure to many ailments. In classical version of BhPr, both exhalation and inhalation humming are alternatively done to complete a breathing cycle. Breath is held in-between inhalation and exhalation. In pranayama techniques according to the yogic texts, holding the breath in-between inhalation and exhalation is said to be very effective. Holding breath after inhalation may give enough time for gas exchange in the lungs and improve ventilation/perfusion ratio matching. Further, holding the breath after exhalation may provide time for the paranasal sinuses to replenish NO after evacuation. We need further experiments to understand this phenomenon and its application for clinical purposes.
The technique of classical BhPr, adding the dimension of specific acoustics to both inhalation and exhalation with appropriate breath-holding in-between may tremendously enhance the expression of NO and cater to its effective end use. This may help to maintain and efficiently regulate the respiratory system; it may also strengthen the respiratory system to boost its overall efficacy.
Inhalation of endogenous NO expressed in the upper airways of the respiratory system, can markedly affect a wide range of processes related to the physiology and pathology. The respiratory airways are provided with the paranasal sinuses that has a significant biological role of producing the major part of NO. NO is involved in regulation of many crucial functions like being the host defense and regulation of pulmonary functions. Experiments have shown that implementing the humming during exhalation and simple yogic concepts of BhPr, offers a unique opportunity to enhance the capacity of the existing anatomical structure in endogenous generation of additional NO. We propose that the other part of classical BhPr i.e., humming during inhalation as defined by the yogic texts may also offer similar results. Understanding the relevance of physical aspects like frequency, resonance and geometry of the paranasal sinuses for NO release in enhancing the prime purpose of the physiological functioning seem to make an enormous difference. This calls for additional studies as it is expected that further advances in this direction may ameliorate the role of NO in fine tuning the regulatory functions, measurement methods, drug delivery systems. Advances in this direction may pave way to development of diagnostic, therapeutic and monitoring processes of several critical respiratory diseases and perhaps help in promoting better health.