2013. The acute hemodynamic effects of blood flow restriction in the absence of exercise.

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Clin Physiol Funct Imaging (2013) 33, pp79–82

doi: 10.1111/j.1475-097X.2012.01157.x

SHORT COMMUNICATION

The acute hemodynamic effects of blood flow restriction in the absence of exercise Jeremy P. Loenneke, Christopher A. Fahs, Robert S. Thiebaud, Lindy M. Rossow, Takashi Abe, Xin Ye, Daeyeol Kim and Michael G. Bemben Neuromuscular Research Laboratory, Department of Health and Exercise Science, The University of Oklahoma, Norman, OK, USA

Summary Correspondence Jeremy P. Loenneke, 1401 Asp Avenue, Room 104. Norman, OK 73019-0615, USA E-mail: [email protected]

Accepted for publication Received 06 May 2012; accepted 29 June 2012

Key words arterial; hypertrophy; KAATSU; safety; venous compliance

The purpose was to investigate the acute effects of blood flow restriction (BFR) on arterial and venous hemodynamic parameters. Nine participants completed a 10-min time control (resting condition) and then a lower body BFR protocol. The protocol was five, 5-min bouts of restrictive cuff inflation with 3-min of deflation between each bout. The pressure was set relative to each individual’s thigh circumference. There were no significant differences between resting and BFR conditions for blood pressure or wave reflection. There was, however, a significant decrease in venous compliance and maximal venous outflow following BFR. Acute BFR with pressures relative to thigh circumference does not result in acute changes in blood pressure or wave reflection. There is, however, an acute decrease in venous compliance and maximal venous outflow, the significance of which is currently unknown. These results suggest that an acute BFR protocol affects venous but not arterial hemodynamics.

Introduction The application of blood flow restriction (BFR) to the lower body induces an orthostatic stress to the body increasing heart and total peripheral resistance (Iida et al., 2007). Such a stimulus has been proposed as a countermeasure to orthostatic intolerance following spaceflight (Iida et al., 2007). Subsequently, many studies have shown repeated bouts of BFR in the absence of exercise to result in an attenuation of both muscle atrophy (measured by MRI and girth) and declines in strength following anterior cruciate ligament reconstruction (Takarada et al., 2000) and cast immobilization (Kubota et al., 2008, 2011).The aforementioned studies utilized an intermittent BFR protocol consisting of five 5-min applications of BFR with 3-min breaks of restriction cuff pressure (cuff deflation). Although beneficial for skeletal muscle, it is currently unknown whether this type of BFR protocol in the absence of exercise affects arterial and venous hemodynamic parameters. Furthermore, no study has investigated these effects using a BFR pressure relative to the participant’s thigh. Thus, the purpose of this study was to investigate the acute effects of BFR on arterial and venous hemodynamic parameters. As BFR restricts venous return while partially reducing arterial inflow, we

hypothesized a reduction in venous compliance and an elevation in heart rate, blood pressure and measures of wave reflection owing to the orthostatic stress. It should be noted that the results from this study are a subset from a different investigation whose main purpose was to investigate the potential mechanisms (muscle cell swelling, metabolic build up, muscle activity) behind BFR in the absence of exercise (manuscript in preparation).

Methods Participants A total of ten (five females and five males) participants visited the laboratory for two sessions of testing. All participants were tested at least 2 h postprandial and were instructed to be hydrated and to avoid caffeine, medications, and exercise on the days of their visits. One female participant felt nauseous from the BFR and did not finish the protocol; therefore, her data were removed from all analyses leaving a final sample size of 9. The study received approval from the university’s institutional review board, and each participant gave written informed consent before participation.

© 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine 33, 1, 79–82

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80 Blood flow restriction, J. P. Loenneke et al.

Study protocol

Blood flow restriction

On the first visit to the laboratory, participants’ height and body mass were measured using a standard stadiometer and an electronic scale. After resting in the supine position for 10 min in a temperature-controlled (22
5°C) room, measurements of brachial blood pressure, thigh circumference (33% distal from inguinal crease) and venous compliance were taken. For the second visit, participants quietly rested for 10 min in the same room as the first visit (22
5°C). Participants sat upright on a table with their upper body inclined at about 45°, their knees fully extended and legs supported on the table. Pillows were placed behind the participants for back support. Participants’ legs were held in position using a padded Velcro wrap to ensure that their legs did not move throughout testing. Blood pressure and wave reflection measurements were taken after 10 min of rest and again approximately 5 min post-BFR cuff removal. Following the initial 10 min of rest, BFR cuffs were attached and inflated for five, 5 min bouts with 3 min of deflation between each bout. This protocol was chosen based on previous research showing an attenuation of muscle atrophy (Takarada et al., 2000; Kubota et al., 2008).

Participants’ wore specially designed pressure cuffs (5 cm wide; Kaatsu-Master, Tokyo, Japan) around the most proximal portion of both legs. The initial cuff pressure (baseline pressure of cuff when deflated) was set at 50 mmHg for all participants. Inflated cuff pressure was relative to the participants’ thigh circumference. Using previous data that suggest thigh circumference as the biggest predictor of arterial occlusion pressure ((Loenneke et al., 2012), n = 116), we plotted thigh circumference with arterial occlusion to determine an estimated arterial occlusion pressure of 70% for each participant (Table 1).

Blood pressure and wave reflection Brachial systolic blood pressure (bSBP) and diastolic (bDBP) blood pressure were measured using an appropriate sized automatic blood pressure cuff (Omron, Model HEM-773). Using a high fidelity strain gauge transducer, radial artery waveforms were obtained at the wrist over a 10-s period (SphygmoCor Model CVMS-CPV; AtCor Medical, Itasca, IL, USA). This pressure waveform was calibrated against the brachial blood pressure, and the software used a generalized transfer function to describe the central (aortic) pressure waveform from which aortic systolic (aSBP), diastolic (aDBP) and mean arterial pressure (MAP) were obtained. Additionally, measures of wave reflection (augmentation index (AIx75) and augmented pressure (AP75) relative to a heart rate of 75) were calculated by the software. Venous compliance Venous compliance of the left calf was measured with venous occlusion plethysmography as described previously (Bleeker et al., 2004). The left leg was elevated (14 cm) above heart level, a blood pressure cuff was placed on the thigh proximal to the knee, and an appropriately-sized strain gauge was placed around the calf at the point of maximum circumference. The pre-BFR measure of venous compliance took place during the first visit to ensure the inflations and deflations from the venous compliance test would not interfere with the primary purpose of another study (in a separate manuscript). Venous compliance measurements for both days were taken at approximately the same time of day (within 1 h) to control for any potential diurnal effect.

Statistical analyses Paired sample t-tests (pre versus post) were used for venous compliance, central pressure, wave reflection and brachial blood pressure. Gender differences for venous compliance have been previously observed (Monahan & Ray, 2004). However, our initial analysis found no gender difference or trend for a difference; therefore, all were pooled into one group for final analysis. An alpha level of 0
05 was used to ascertain significant differences between means and variability is presented as standard deviation.

Results The mean age, height, body mass and thigh circumference for the participants were 25 (3) years, 1
75 (0
10) m, 76
3 (12
5) kg and 58
2 (4
7) cm, respectively. There were no significant differences between Pre-CON and 5 min Post-BFR cuff removal with bSBP (Pre 121 (7) versus Post 118 (10) mmHg, P = 0
37), bDBP [Pre 74 (7) versus Post 78 (6) mmHg, P = 0
08], MAP [Pre 89 (6) versus Post 90 (7) mmHg, P = 0
53], aSBP [Pre 105 (6) versus Post 104 (9) mmHg, P = 0
89], aDBP [Pre 75 (7) versus Post 79 (6) mmHg, P = 0
10], AP75 [Pre-1 (3) versus Post-1 (3), P = 0
26] or AIx75 [Pre-3 (11) versus Post-6 (14, P = 0
15)]. There was, however, a significant decrease in venous compliance following BFR (Fig. 1, P = 0
007). Fig. 2 depicts the significant Table 1 Blood flow restriction pressures. The pressures used for this study were based on thigh circumference (thigh circ.) data from a previous investigation (adapted from Loenneke et al., 2012). We used 70% of the estimated arterial occlusion pressure to make the stimulus more uniform between participants.

Thigh circ. (cm)

Estimated arterial occlusion pressure (mmHg)

Pressure used (70%) (mmHg)

< 45–50 51–55 56–59 > 60

200 250 300 350

140 180 210 250

© 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine 33, 1, 79–82

Blood flow restriction, J. P. Loenneke et al. 81

Figure 1 Venous compliance. Pressure–volume curves for the calf before (Pre) and after (Post) blood flow restriction protocol; VVV, venous volume variation. Venous compliance (Vc) is derived from the slope of the pressure–volume curve. *P < 0
05 pre versus post.

Figure 2 Maximal venous outflow. Maximal venous outflow (MVO) of the calf before (Pre) and after (Post) blood flow restriction protocol. Pv = venous pressure. *P < 0
05 pre versus post.

decrease in maximal venous outflow at 20 (P = 0
021), 40 (P = 0
025), 60 (P = 0
023) and 80 (P = 0
026) mmHg 10 min after a bout of BFR.

(P = 0
08) and central DBP (P = 0
10). This is similar to the findings of Iida et al. (2007) who observed increases in peripheral DBP following BFR at 150 and 250 mmHg pressures. It is difficult to directly compare our study with that investigation as they used two separate cuffs interchangeably, which has been shown to result in different responses in blood flow (Loenneke et al., 2012). Regardless, the trend for an increase in DBP might reflect a slight increase in peripheral resistance because of the acute perturbations in blood flow. Our results demonstrate that within 5 min of cuff removal any changes that might have occurred with acute BFR are back to baseline. The acute decreases observed with venous compliance and maximal venous outflow are similar to those observed with lower body negative pressure in men (Fu et al., 2002). This may be due to a reduction in central blood volume, which would unload the baroreceptors. An unloading of the baroreceptor would increase sympathetic activity resulting in an increase in smooth muscle tone, which can reduce venous compliance (Greaney & Farquhar, 2011). However, research from Sielatycki et al. (2011) found that an adrenergic blockade did not have an effect on venous compliance, suggesting that local factors such as endothelin and/or myogenic tone may be playing more of a functional role (Greaney & Farquhar, 2011). Further evidence for a local response is the lack of correlation between percentage changes in plasma volume and venous compliance (data not shown). One potential limitation from this study was that venous compliance measurements were completed on separate days as to not interfere with the primary purpose of another study which was to investigate potential fluid shifts into skeletal muscle following the application of BFR (in a separate manuscript). Furthermore, although measurements were taken at the same time of day, we cannot rule out daily variation in compliance. Finally, this study was only completed on nine participants; therefore, future investigations should investigate this stimulus on a larger cohort to better determine its absolute impact on the heart. In conclusion, no acute changes in blood pressure or wave reflection occur with acute BFR. There is, however, an acute decrease in venous compliance and maximal venous outflow, the significance of which is currently unknown but may indicate that BFR can potentially provide a countermeasure for orthostatic intolerance.

Discussion This investigation found no changes from Pre-BFR to 5 min post-BFR in peripheral/central blood pressure or wave reflection. This indicates that an acute bout of BFR does not negatively impact the pressure at the heart which is important because this modality has the greatest potential benefit for clinical populations. We did, however, observe a small non-significant but possibly physiological increase in peripheral

Acknowledgment This study was not supported by any funding.

Conflict of interest No author reported a conflict of interest with research presented in the manuscript.

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82 Blood flow restriction, J. P. Loenneke et al.

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© 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine 33, 1, 79–82