Objetivo y campo de aplicación 1 Objetivo

This review included 49 studies involving 1698 experimental subjects with study durations ranging from a single session to six months. A total of 11 RCTs were located with all of them having a Jadad score of 3 or less. A flow chart of the study search including the numbers of papers identified is shown in Figure 7.6. Studies, categorised according to the type of intervention (relaxation/meditation, pranayama practice, integrated yoga/asana practice) are presented in Tables 7.6.1- 7.6.3(b).

Review

132

7.6.1 HRV and Yogic Relaxation or Meditation

Table 7.6.1 summarises the 10 studies investigating HRV with yoga relaxation and/or meditation. Six of these studies are laboratory-based studies involving regular yoga/meditation practitioners, while four studies are ranging from 6 weeks to over 6 months. These studies, which include 521 participants, reported varied outcomes with 6 studies reporting increases in HRV during yoga relaxation and/or meditation and 4 studies reporting no change.

Five studies compared HRV at baseline with HRV during or after a single laboratory session of yoga relaxation or meditation practice in regular yoga practitioners while a further study compared HRV during different stages of meditation. Of these studies, three reported reduced LFn.u and increased HFn.u

Studies identified in primary search (n= 127) Studies identified through bibliography searches (n=11) Total studies (n= 138)

Non English Literature (n=4)

Unobtainable (n=9) Protocol (n=3) Did not include data on HRV (n=8)

Review (n=2)

Letters and reports (n=4)

Finally selected studies (n=49)

 Meditation/Relaxation (n= 10)  Pranayama (n=15)  Asana/Integrated yoga (n=24) Id en ti fi ca ti o n In cl u d e d Duplicate articles (n= 36)

(Figure: 7.6) Flow Chart of Study Search and Included Studies

Filtered Studies (n=102)

Relevant studies for the

review (n=49) Sc re e n in g/ el igi b ili ty

133 (Markil et al. 2012; TellesRaghavendra, et al. 2013; Vempati, R & Telles 2002), while two different studies that investigated Transcendental Meditation in advanced meditators and reported increased HF amplitude(ms2_{) during}

periods of meditation compared to baseline eyes closed (Travis & Wallace 1999) and during period of transcending experience compared to other experiences during meditation (Travis 2001). The one study examining HRV during meditation (dhayana), focused thinking (dharana), non-meditative thinking (ekagrata) and random thinking (cancatla), reported reduced LFn.u and increase HFn.u during meditation (dhyana) and an increased LFn.u and reduced HFn.u during non-meditative thinking and random thinking (TellesRaghavendra, et al. 2013). Furthermore, one study that compared HRV at baseline with HRV after yoga relaxation reported no change in HRV (Vempati, R & Telles 1999).

Of the three randomised studies, one study of coronary heart disease patients (with Jadad score 3) reported a marginal increase in HF-HRV ms2

(p<.07) after 16 weeks of Transcendental Meditation compared to a control group that received heath education (Paul-Labrador et al. 2006). Of the two randomised controlled trials reporting no change in HRV, one (with Jadad score 3) reported no change after 10 weeks of Transcendental Meditation (Travis et al. 2009) while another (with Jadad score 2) reported no change in HRV with 6 months of yoga relaxation practice (Monika et al. 2012). Additionally, a non-randomised controlled trial of adolescents reported no change in HRV after 6-weeks of yoga relaxation practice (Madanmohan 2004).

7.6.2 HRV and Yoga Breathing

Table 7.6.2 (a) summarises 5 studies that involved rapid breathing practices. The two studies that measured HRV during rapid Kapalbhati breathing reported decreases in LFms2 _{and HFms}2 _{(Peng et al. 2004; Stancak et al. 1991), while the}

two studies that compared HRV before and after Kapalbhati breathing reported increased LFn.u. and reduced HFn.u. (Raghuraj et al. 1998), or no change in LFn.u and HFn.u but a reduction in proportion of NN50 (pNN50) after the practice (Telles, Singh & Balkrishna 2011). The only longitudinal study was an RCT (with Jada Score 2) of elderly people regularly performing Bahstrika (rapid shallow breathing) that compared HRV before and after a 4-month intervention period.

Review

134 This study, which measured HRV during a period of regulated breathing at 12 BPM reported decreases in LFn.u. and LF/HF in the breathing group compared to controls (Santaella et al. 2011).

Table 7.6.2 (b) summarises the 11 studies that involved slow breathing practices, nine of these studies were laboratory based, while one was a longitudinal cohort study involving non-yoga practitioners and one a non- randomised controlled trial with chronic obstructive pulmonary diseases (COPD) patients. Eight of these studies either regulated breathing at a breath rate between 1-9 BPM, or allowed spontaneous breathing with a rate below 9 BPM.

Eight laboratory based studies compared HRV before, and either during or after various slow breathing practices. Of these two studies report increases in LFms2 _{(Ghiya & Lee 2012; Peng et al. 2004) and two report increases in LFn.u.}

with increase in LF/HF observed during breathing practice (Ghiya & Lee 2012; Peng et al. 2004; Raghuraj & Telles 2008; Raghvendra 2013) while one study report increased HR oscillations in LF band (Peng et al. 1999). Similar increased HR oscillation in LF Band significant decrease in respiratory frequency was also reported during mantra chanting and rosary prayer compared to post-session spontaneous breathing (BernardiSleight, et al. 2001). The one study that examined extremely slow breathing at 1 BPM in a single practitioner, reported an increase in VLFms2 _{and LF/HF and corresponding increases in HR while also}

reporting reductions in LFms2 _{and HFms}2 _{(Jovanov 2005). A further study that}

compared HRV in yoga practitioners and non-practitioners during deep slow breathing at 6 BPM reported higher Standard deviation of NN intervals ‘(SDNN), root mean square of successive differences (RMSSD) and the number of pairs of successive NNs that differ by more than 50ms (NN50) in yoga practitioners during the practice (Muralikrishnan et al. 2012).

Two studies examined combinations of breathing that include both fast and slow breathing practices. These studies report increased LFms2 _{and reduced}

RMSSD during the practices (Selvaraj et al. 2008) and decreased sympatho-vagal balance with increased HFn.u and reduced LFn.u. outflow to the heart after 2 months of regular practise (Bhimani et al. 2011). A further 3 months study

135 reported no change in HRV in COPD patients and healthy controls with yoga breathing (Jaju et al. 2011).

7.6.3 HRV and Yoga Postures and Integrated Yoga

Table 7.6.3 (a) summarises 21 studies that investigated either yoga postures or integrated yoga practices that combine postures breathing and meditation. The majority of these studies report enhanced autonomic balance with yoga practices. Of the 3 RCTs (only one with Jadad score of 3) one RCT with 24 participants (Patil et al. 2013) and two RCT’s, each with more than 60 female participants (Huang, FJ, Chien & Chung 2013; Satyapriya et al. 2009), report increased HFn.u. and decreased LFn.u. and LF/HF ratio with regular integrated yoga practise. A decrease in LFms2_{was also reported in a 8 week longitudinal cohort study of}

depressive patients practicing Iyenger yoga (Shapiro et al. 2007) and an increase in pNN50 was reported after 8 weeks practicing inverted or semi inverted yoga postures (Papp et al. 2013).

Of the reviewed laboratory studies, four involved cyclic meditation, which involves a series of postures interspersed with relaxation practices. Three of these studies report increased HFn.u and decreased LFn.u along with decreased LH/HF ratio post intervention compared to baseline (An et al. 2010; Sarang & Telles 2006; Vempati, RR, Telles, S. 2000), while one reported higher sympathovagal balance and lower LFn.u during sleep after the practice of cyclic medication compared to rest (Patra & Telles 2010). Further laboratory studies reported a decreased LH/HF ratio with yoga inversion postures (Howorka et al. 1995) and increased time domain indicators of vagal activities with Iyenger yoga (Khattab et al. 2007), laughter yoga (Dolgoff-Kaspar et al. 2012), chair-based yoga practise (Melville et al. 2012) and integrated yoga (Shankarappa & Prabha 2013).

In contrast to these results, one study reported increased LF/HF ratio indicating decreased autonomic balance after performing yoga headstands (Manjunath & Telles 2003) and six studies, reported no change in HRV with various other yoga practices. This includes four RCTs of integrated practices (only one of which had Jadad scores of 3) involving less than 40 subjects (Bidwell et al. 2012; Bowman, Clayton & Murray 1997; Cheema et al. 2013; Telles et al. 2010),

Review

136 one non-RCT with hypertensive patients (Niranjan et al. 2009), and a small cohort study of 11 hypertensive patients and 6 diabetic patients practicing integrated yoga for 7 days (Singh & Telles 2009).

Table 7.6.3 (b) summarises four studies comparing HRV in the resting state in non-yoga practitioners and regular yoga practitioners. Three of these studies report enhanced parasympathetic activity measured in time and/or frequency domain in regular yoga practitioners (Friis & Sollers Iii 2013; Muralikrishnan et al. 2012; Satin, Linden & Millman 2013) compared to non-yoga practitioners, while one study reported lower parasympathetic activity in regular practitioners compared to non-practitioners (Chaya, MS et al. 2008).