Effect Of Blood Flow Occlusion Research Articles

The use of blood flow restriction does not enhance adaptations of corticospinal excitability or intracortical inhibition after acute resistance training

Resistance exercise with blood flow restriction (BFR) is considered a safe and powerful training tool. Low-load (LL) resistance training with BFR results in comparable hypertrophy compared to conventional heavy-load (HL) resistance training (Centner et al., 2019). Additionally, LL training with BFR (LL-BFR) induces comparable (Grønfeldt et al., 2020) or slightly lower (Centner et al., 2019) effects on muscle strength than HL training. It is generally accepted that increases in maximum strength are mediated by muscular hypertrophy and/or neural adaptations. However, the effect of BFR on neural adaptations is scarcely investigated. The aim of this study was therefore to investigate the effects of BFR on acute neural adaptations following a single bout of resistance training.
 Fifteen male participants (21-35 years) volunteered to participate in this study. On three separate days, participants performed a strength training session of the right elbow flexors with either LL, LL-BFR or HL. Neuromuscular adaptations were investigated before and after each resistance training session by means of transcranial magnetic stimulation (single- and paired-pulse TMS) and peripheral nerve stimulation (Mmax). Data were acquired during submaximal sustained isometric contractions. During LL-BFR, the cuff was inflated to 50% of the individual arterial occlusion pressure to restrict venous outflow in the working musculature during exercise.
 The preliminary data analysis with mixed linear models revealed that, compared to baseline values, normalized MEPs (% of Mmax) from the trained biceps brachii were enhanced for HL (Cohen’s d = 0.51) but not LL-BFR (Cohen’s d = 0.03) when compared to LL. None of the groups showed relevant changes in short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). The size of Mmax decreased slightly for HL (Cohen’s d = -0.18) but not LL-BFR (Cohen’s d = 0.06) when compared to LL.
 This is the first study that investigated acute neural adaptations in response to resistance training with and without BFR. We observed increased MEP amplitudes after HL but not LL what is in line with previous evidence (Mason et al., 2019). Since training with BFR results in a rapid increase in motoneuronal excitability (Copithorne et al., 2020), the increased MEP are less likely caused by changes at the cortical site.
 Centner, C., Wiegel, P., Gollhofer, A., & König, D. (2019). Effects of blood flow restriction training on muscular strength and hypertrophy in older individuals: A systematic review and meta-analysis. Sports Medicine, 49, 95-108. https://doi.org/10.1007/s40279-018-0994-1
 Copithorne, D. B., Rice, C. L., & McNeil, C. J. (2020). Effect of blood flow occlusion on corticospinal excitability during sustained low-intensity isometric elbow flexion. Journal of Neurophysiology, 123(3), 1113-1119. https://doi.org/10.1152/jn.00644.2019
 Grønfeldt, B. M., Lindberg Nielsen, J., Mieritz, R. M., Lund, H., & Aagaard, P. (2020). Effect of blood-flow restricted vs heavy-load strength training on muscle strength: Systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 30(5), 837-848. https://doi.org/10.1111/sms.13632
 Mason, J., Howatson, G., Frazer, A. K., Pearce, A. J., Jaberzadeh, S., Avela, J., & Kidgell, D. J. (2019). Modulation of intracortical inhibition and excitation in agonist and antagonist muscles following acute strength training. European Journal of Applied Physiology, 119, 2185-2199. https://doi.org/10.1007/s00421-019-04203-9

The effect of blood flow on tibialis anterior motor unit firing rates during sustained low-intensity isometric contractions.

Low-intensity contractions with blood flow occlusion (BFO) result in neuromuscular adaptations comparable with high-intensity (>70% maximal voluntary contraction, MVC) exercise. Because BFO exercise can only be applied to limb muscles, it is of interest to explore whether muscles proximal to the occlusion site are affected. Therefore, the purpose of this study was to assess neural activation of the tibialis anterior (TA) when flow is occluded proximal and distal to the active muscle. Five males completed three protocols to observe the effect of BFO on motor unit firing rates (MUFR) of the TA at a fatiguing contraction intensity of ∼15% MVC. Two occlusion protocols, one proximal (BFOprox) to and one distal (BFOdis) to the TA, were compared with a control (free-flow) protocol time-matched to BFOdis. MVC was significantly reduced following the BFOprox (∼41%; P< 0.001) and BFOdis (∼27%, P< 0.001), but not following the control protocol (∼15%; P= 0.13). Surface electromyography (EMG) during BFOdis and BFOprox increased ∼14% and ∼28%, respectively, but was not different among protocols. MUFRs for BFOdis and BFOprox were significantly reduced (by ∼33% and ∼23%, respectively; P< 0.01) at task failure. Results indicate that although BFOprox results in the largest reductions of MUFRs, BFOdis shows greater impairments compared with the free-flow control condition. Novelty Effects on motor unit firing rates of proximal versus distal blood flow occlusion were compared during low-intensity fatiguing task. Proximal occlusion results in greatest fatigue and reduction in motor unit rates, but distal occlusion elicits more fatigue and rate reduction than a control task.

Effect of blood flow occlusion on corticospinal excitability during sustained low-intensity isometric elbow flexion.

Blood flow occlusion (BFO) has been used to study the influence of group III/IV muscle afferents after fatiguing exercise, but it is unknown how BFO-induced activity of these afferents affects motor cortical and motoneuronal excitability during low-intensity exercise. Therefore, the purpose of this study was to assess the acute effect of BFO on peripheral [maximal M wave (Mmax)], spinal [cervicomedullary motor evoked potential (CMEP) normalized to Mmax], and motor cortical [motor evoked potential (MEP) normalized to CMEP] excitability. Nine healthy men completed a sustained isometric contraction of the elbow flexors at 20% of maximal force under three conditions: 1) contractile failure with BFO, 2) a time-matched trial without restriction [free flow (FFiso)], and 3) contractile failure with free flow (FFfail). Time to failure for BFO (and FFiso) were ~80% shorter than that for FFfail (P < 0.05). For FFfail and FFiso, Mmax area decreased ~17% and ~7%, respectively (P < 0.05), with no change during BFO. CMEP/Mmax area increased ~226% and ~80% during BFO and FFfail, respectively (P < 0.05), with no change during FFiso (P > 0.05). The increase in normalized CMEP area was greater for BFO and FFfail compared with FFiso and for BFO compared with FFfail. MEP/CMEP area was not different among the protocols (P > 0.05) and increased ~64% with time (P < 0.05). It is likely that group III/IV muscle afferent feedback to the spinal cord modulates the large increase in motoneuronal excitability for the BFO compared with FFfail and FFiso protocols.NEW & NOTEWORTHY We have observed how blood flow occlusion modulates motor cortical, spinal, and peripheral excitability during and immediately after a sustained low-intensity isometric elbow flexion contraction to failure. We conclude that blood flow occlusion causes a greater and more rapid increase in motoneuronal excitability.

Effect of blood flow occlusion on neuromuscular fatigue following sustained maximal isometric contraction.

Sustained isometric maximal voluntary contractions (IMVCs) have blood flow occlusive effects on the microvasculature. However, it is unknown if this effect would be magnified with additional blood flow restriction via a cuff and what the influence on fatigue development would be. Twelve healthy male participants performed a 1-min IMVC of the knee extensors with and without additional blood flow occlusion induced by pneumatic cuff in counterbalanced order on separate days. Vastus lateralis muscle deoxygenation was estimated via near-infrared spectroscopy-derived tissue oxygen saturation (SmO2) throughout the fatiguing contraction. Central and peripheral measures of neuromuscular fatigue (NMF) were assessed via surface electromyography (EMG) and force responses to voluntary contractions and peripheral nerve/transcranial magnetic stimulations before, immediately after, and throughout an 8-min recovery period. SmO2, force, and EMG amplitude decreased during the 1-min IMVC, but there were no between-condition differences. Similarly, no significant (p > 0.05) between-condition differences were detected for any dependent variable immediately after the fatiguing contraction. Transcranial magnetic stimulation (TMS)-derived voluntary activation was lower (p < 0.05) in the no-cuff condition during the recovery period. Sustained IMVC results in a similar degree of muscle deoxygenation and NMF as IMVCs with additional occlusion, providing further evidence that a sustained IMVC induces full ischemia. Novelty NMF etiology, muscle oxygenation, and corticospinal factors during an IMVC are similar with or without an occlusion cuff. Contrary to all other measures, TMS-evaluated voluntary activation returned to baseline faster following the occluded condition.

The effect of blood flow occlusion during acute low-intensity isometric elbow flexion exercise.

Blood flow restriction (BFR) with low-intensity (< 30% of 1 repetition maximum strength) muscle contraction has been used chronically (> 4weeks) to enhance resistance training. However, mechanisms underlying muscle adaptations following BFR are not well understood. To explore changes related to chronic BFR adaptations, the current study used blood flow occlusion (BFO) during an acute bout of low-intensity isometric fatiguing contractions to assess peripheral (muscle) factors affected. Ten males completed separate fatiguing elbow flexor protocols to failure; one with BFO and one with un-restricted blood flow (FF). Baseline, post-task failure, and 30min of recovery measures of voluntary and involuntary contractile properties were compared. BFO had greater impairment of intrinsic measures compared with FF, despite FF lasting 80% longer. Following task failure, maximal voluntary contraction and 50Hz torque decreased in both protocols (~ 60% from baseline). Voluntary activation decreased ~ 11% from baseline at failure following both protocols, but recovered at a faster rate following BFO, whereas MVC recovered to ~ 90% of baseline in both protocols. The 10/50Hz torque ratio was decreased by ~ 68% and ~ 21% from baseline, for BFO and FF, respectively (P < 0.01). 50Hz half-relaxation-time (HRT) was significantly longer immediately following BFO (~ 107% greater than baseline), with no change following FF. Thus, greater peripheral fatigue that recovers at a similar rate compared to conventional exercise is likely driving muscle adaptations observed with chronic BFR exercise. Likely BFO alters energy demand and supply of working muscle similar to chronic BFR, but is exaggerated in this paradigm.

Evaluation of recovery from local muscle fatigue by voluntary test contractions.

The applicability of surface EMG frequency analysis as a means of evaluating recovery from local muscle fatigue was studied experimentally, fatigue being given as the proportion of the integrated value of frequency components below 60 Hz to that of all components. When the maximum voluntary contractions of elbow flexor were done repeatedly in the recovery period after dynamic or static contractions, the slow wave proportion recovered to the initial value within about 6 min after work. The muscle force of test contraction after 20 min or more was, however, still significantly lower than its initial value. Recovery of integrated EMG value was faster than that of muscle force but slower than that of slow wave components. The effect of blood flow occlusion on the recovery was then tested using different levels of load. When the occlusion was made for 4 min immediately following the sustained contractions, the slow wave component again increased after a phase of decrease but did not reach the final level attained at the end of work, implying that the observed changes in EMG frequency were somewhat related to local muscular fatigue of a peripheral nature. The recovery from local muscular fatigue may thus be evaluated by intermittent brief test contractions after muscular work.

Influence of selective hemihepatic blood flow occlusion on long-term survival following liver resection for metastasis of colorectal cancer

Objective To explore the clinical effect of selective hemihepatic blood flow occlusion in hemihepatectomy for metastasis of colorectal cancer.Methods The clinical data of 71 cases of me-tastatic cancer of the liver surgically treated in our hospital from 1998 to 2006 were retrospectively analyzed.Surgical effect was compared between the selective hemihepatic blood flow occlusion group and the Pringle group.Results The 1-, 3-, and 5-year survival rates for all the patients were 82.7%, 46.20% and 27.1%, respectively.They were 89.7 %, 54.2 %, 34.1% in the selective hemihepatic blood flow occlusion group and 73.3%,41.5% ,23.9% in the Pringle group, respectively.There were sig-nificant differences between the 2 groups (P<0.05).Conclusion The hepatectomy for the metastasis in the liver of eolorectal cancer by hemihepatic blood flow occlusion is a more effective procedure to prolong the long-term survival than by Pringle procedure. Key words: Hepatectomy; Selective hemihepatic blood flow occlusion; Colorectal metastases

Effect of Blood Flow Occlusion on Laser Hyperthermia for Liver Metastases

Background. Interstitial laser hyperthermia (ILH) is an in situ ablative technique for the treatment of colorectal liver metastases. A significant factor limiting tumor destruction is hepatic blood flow. Modulation of hepatic blood flow may increase the size of tumor necrosis achieved. Our aim was to investigate the effect of blood flow occlusion on ILH-induced necrosis in both tumor and normal liver tissue.Materials and methods. A model of colorectal liver metastases in male inbred CBA mice was used. ILH was applied to normal liver and tumor tissue using a bare optical quartz fiber from an SYL500 Nd:YAG surgical laser generator, with and without hepatic blood flow occlusion, and the extent of necrosis was studied. Tumor blood flow was assessed by laser Doppler flowmetry and scanning electron microscopy.Results. Hepatic blood flow occlusion resulted in a significant reduction in blood flow in normal liver tissue (37.9% ± 5.8, P < 0.001) and in the periphery of the tumor (17.5% ± 7.8, P < 0.001). It did not affect the blood flow in the center of the tumor (13.4% ± 4.3, P = 0.07). ILH of normal liver tissue, at low power (2 W), with hepatic blood flow occlusion, resulted in a significant increase in the diameter of necrosis. This effect was not seen when higher power (5 W) was used in normal liver. No significant effect was noted within tumor tissue at either power setting.Conclusion. The overall effect of hepatic blood flow occlusion in ILH-induced tissue necrosis appears to be negligible in tumor tissue. Its main applicability appears to be at the tumor–host interface, where a decrease in blood flow may lead to higher temperatures and therefore to a greater degree of tumor cell destruction.