Middle cerebral artery velocity during head-up tilt induced hypovolemic shock in humans

Summary. Middle cerebral artery mean velocity (V_mean) and pulsatility index (PI) were followed during head-up tilt induced hypovolaemic shock in nine subjects. Mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP) and thoracic (TI) electrical impedance were also recorded. V_mean, PI, and CVP did not change during head-up tilt to 50°, while MAP increased from 92 (81–106) (median and range) to 100 (97–112) mmHg, HR from 63 (53–74) to 84 (68–89) beats min^-1 and Tl_100kHz from 30 (27–36) to 32 (30–39) Ohm (P < 0.01) (n= 8). During maintained tilt, V_mean decreased from 52 (32–72) to 34 (16–59) cms^-1, whereas HR increased to 87 (52–108) beats min^-1 and Tl_100kHz to 33 (31–39) Ohm (P < 0.01). Presyncopal symptoms appeared after 33 (3–46) min and were associated with a MAP of 65 (32–84) mmHg (P < 0.01) and a HR of 58 (52–71) beats min^-1 (P < 0.05).V_mean decreased to 25 (16–36) cms^-1, and cerebral conductance index (V_mean/MAP_brain) and PI increased (P < 0.01). Arterial collapse was observed (diastolic velocity of zero) in one subject at a brain (diastolic) blood pressure of 21 mmHg and he developed tachycardia (131 beats min^-1) during presyncope. P_aCO₂ did not change. Maintained tilt resulted in central volume depletion reflected by changes in MAP, HR, and thoracic electrical impedance but not in CVP. Transcranial Doppler derived indices of cerebral perfusion demonstrated critically low values despite marked increase in conductance index.     

Middle cerebral artery blood velocity during exercise in patients with atrial fibrillation

Atrial fibrillation limits the ability to increase cardiac output during exercise and may, in turn, affect the exercise-associated elevation in cerebral perfusion. In nine patients with atrial fibrillation (AF) and in five age-matched healthy subjects, middle cerebral artery blood velocity (MCA V_mean) was measured during incremental exercise using the transcranial Doppler. The AF patient group exhibited a lower aerobic capacity than the control group [peak work rate: 106 W (71–153 W; median and range) vs. 129 W (118–159 W) and maximal oxygen uptake: 1·4 l min^–1 (1·0–1·9 l min^–1) vs. 1·7 l min^–1 (1·4–2·2 l min^–1); P = 0·05]. At rest, MCA V_mean was not significantly different between the two groups [43 cm s^–1 (39–56 cm s^–1) vs. 52 cm s^–1 (40–68 cm s^–1)]. During intense cycling, the increase in MCA V_mean was to 51 cm s^–1 (40–78 cm s^–1) (9%) in the AF group and lower than in the healthy subjects [to 62 cm s^–1 (50–81 cm s^–1) 23%; P<0·05], which corresponded with the smaller than expected increase in cardiac output [156% (130–169%) vs. 180%]. Thus, there was a correlation between the increase in MCA V_mean and the ability to increase cardiac output (r² = 0·55, P<0·01). We suggest that, during exercise with a large muscle mass, atrial fibrillation affects the ability to elevate cerebral perfusion, and this results from an impaired ability to increase cardiac output.     

The effect of positive end-expiratory pressure ventilation on propofol concentrations during general anesthesia in humans

The present study investigated the effects of positive end-expiratory pressure (PEEP) on propofol concentrations in humans. Eleven patients undergoing elective surgery were enrolled in this study. Anesthesia was induced with propofol, then maintained using 60% nitrous oxide in oxygen, fentanyl 10-20 microg/kg and continuous infusion of propofol. Vecuronium was used to facilitate the artificial ventilation of the lungs. Propofol was administered to all subjects via target-controlled infusion to achieve a propofol concentration of 6.0 microg/mL at intubation and 2.0 microg/mL after intubation. Before, during and after PEEP level of 10 cmH(2)O, cardiac output (CO) and effective liver blood flow (LBF) was measured using indocyanine green as an indicator and blood propofol concentration was determined using high-performance liquid chromatography. Data are expressed as median and range. After PEEP of 10 cmH(2)O was applied, CO and effective LBF was significantly decreased from 5.5 (3.8-6.8) L/min to 4.5 (3.2-5.8) L/min (P < 0.05), 0.78 (0.65-1.21) L/min to 0.65 (0.50-0.89) L/min (P < 0.05), respectively. Propofol concentration was significantly increased from 2.21 (1.46-2.63) microg/mL to 2.45(1.79-2.89) microg/mL (P < 0.05). These data indicate that propofol concentrations can be increased by PEEP, suggesting the possibility of overdosing following PEEP.     

Blood volume distribution during head-up tilt induced central hypovolaemia in man

Summary. We evaluated regional electrical impedance (Z°) at 2.5 and 100 kHz to separate intra- and extracellular fluid changes and correlated Z° over the thorax (TI) to relative changes in the central blood volume (CBV) induced by head-up tilt. In nine experiments head-up tilt resulted in normotensive central hypovolaemia associated with a 3·7 & 0·4 Ohm (mean f SE) increase in TI_{100 kHz} after 60 min. In 24 experiments presyncopal symptoms were induced after 43±2 min, when TI_100kHz had increased 4·2 ± 0·2 Ohm. Head-up tilt instantly decreased the activity of technetium labelled erythrocytes (⁹⁹Tc^m) over the thorax by 24 ± 2%, and increased ⁹⁹Tc^m over the thigh by 68±10% (P< 0·01, n = 8) with no further changes during the sustained tilt. Haematocrite increased during head-up tilt from 43·1 ± 0·3 to 47·9 ± 0·6% (P<0·01, n= 8). Accordingly, the increase in TI (6·3 ± 0·6 vs. 4·5 0·4 Ohm, n= 6) and the decrease in Z° through one leg (7·2 ± 1·2 vs. 2·8 ± 0·5 Ohm, n= 6) at 2·5 kHz was more pronounced than at 100 kHz. Also the changes in TI were correlated to CBV as calculated from ⁹⁹T_c^m and haematocrite (r = 0.90, P < 0·01). The results suggest that: (1) Hypovolaemic shock is associated with a faster increase of TI than normotensive head-up tilt. (2) Head-up tilt is characterized by an initial decrease in CBV followed by a further decrease in plasma volume, which eventually leads to hypovolaemic shock. (3) Blood volume changes during head-up tilt are reflected in regional Z°.     

The C-terminal fragment of big endothelin-1 does not potentiate the vasoactive effects of endothelin-1

The aim was to study the cardiovascular effects of the C-terminal (22–38) fragment of big endothelin-1, which is produced by the cleavage of big endothelin-1 (big ET-1) to endothelin-1 (ET-1). An intravenous infusion of the (22–38) fragment (4, 8 and 12 pmol kg^?1 min^?1, each dose for 10 min) was given to 10 healthy subjects. Four control subjects received 0·9% saline. Two additional subjects received ET-1 (0·2 and 4 pmol kg^?1 min^?1, each dose for 20 min) alone or combined with an equimolar infusion of the (22–38) fragment on two separate occasions. The fragment infusion did not alter heart rate, mean arterial blood pressure, cardiac output, systemic or pulmonary vascular resistance, splanchnic, cerebral or forearm blood flow. Renal blood flow showed a slight fall (11%, P<0·001) in the fragment group of the same magnitude as in a previous control study. After the fragment infusion, a decrease in mean pulmonary arterial pressure (MPAP) by 12% (P<0·01) and in pulmonary capillary wedge pressure (PCWP) by 31% (P<0·001) was noted, which did not differ from the pulmonary pressures in the saline-infused control group. The (22–38) fragment, when combined with ET-1, was not able to modify the effects of ET-1 on heart rate, mean arterial blood pressure, splanchnic and renal blood flow. Consequently, the exogenous (22–38) fragment does not seem to cause any significant cardiovascular effects in healthy humans.     

Validation of non‐invasive haemodynamic methods in patients with liver disease: the Finometer and the Task Force Monitor

Patients with advanced cirrhosis often present a hyperdynamic circulation characterized by a decrease in systolic and diastolic blood pressure (SBP and DBP), and an increase in heart rate (HR) and cardiac output (CO). Accurate assessment of the altered circulation can be performed invasively; however, due to the disadvantages of this approach, non‐invasive methods are warranted. The purpose of this study was to compare continuous non‐invasive measurements of haemodynamic variables by the Finometer and the Task Force Monitor with simultaneous invasive measurements. In 25 patients with cirrhosis, SBP, DBP and HR were measured non‐invasively and by femoral artery catheterization. CO was measured non‐invasively and by indicator dilution technique. The non‐invasive pressure monitoring was considered acceptable with a bias (accuracy) and a SD (precision) not exceeding 5 and 8 mmHg, respectively, as recommended by the Association for the Advancement of Medical Instrumentation. The accuracy and precision of the Finometer and the Task Force Monitor were as follows: SBP: ?3·6 ± 17·9 and ?8·9 ± 17·5 mmHg, respectively; DBP: 4·2 ± 9·6 and 1·9 ± 8·6 mmHg, respectively; HR: 2·0 ± 6·9 and 2·2 ± 6·2 bpm, respectively; and CO: 0·1 ± 1·6 and ?1·0 ± 2·0 L min^?1, respectively. The study demonstrates that the overall performances of the Finometer and the Task Force Monitor in estimating absolute values of SBP, DBP, HR and CO in patients with cirrhosis are not equivalent to the gold standard, but may have an acceptable performance with repeated measurements.     

Forearm–finger skin temperature gradient as an index of cutaneous perfusion during steady‐state exercise

The purpose of this study was to examine whether the forearm–finger skin temperature gradient (T_{forearm–finger}), an index of vasomotor tone during resting conditions, can also be used during steady‐state exercise. Twelve healthy men performed three cycling trials at an intensity of ~60% of their maximal oxygen uptake for 75 min separated by at least 48 h. During exercise, forearm skin blood flow (BF_F) was measured with a laser‐Doppler flowmeter, and finger skin blood flow (PPG) was recorded from the left index fingertip using a pulse plethysmogram. T_{forearm–finger} of the left arm was calculated from the values derived by two thermistors placed on the radial side of the forearm and on the tip of the middle finger. During exercise, PPG and BF_F increased (P<0·001), and T_{forearm–finger} decreased (P<0·001) from their resting values, indicating a peripheral vasodilatation. There was a significant correlation between T_{forearm–finger} and both PPG (r = ?0·68; P<0·001) and BF_F (r = ?0·50; P<0·001). It is concluded that T_{forearm–finger} is a valid qualitative index of cutaneous vasomotor tone during steady‐state exercise.     

Blood perfusion changes during sacral nerve root stimulation versus surface gluteus electrical stimulation on in seated spinal cord injury

The objective of this article is to examine dynamic changes of ischial blood perfusion during sacral nerve root stimulation against surface functional electrical stimulation (FES). Fourteen adults with suprasacral spinal cord injury (SCI) were recruited. The gluteal maximus was activated by surface FES or stimulating sacral nerve roots by functional magnetic stimulation (FMS) or a sacral anterior root stimulator implant (SARS). Ischial skin index of hemoglobin (IHB) and oxygenation (IOX) was measured.Skin blood perfusion was significantly higher during FMS than the baseline (IHB 1.05 ± 0.21 before vs.1.08 ± 0.02 during stimulation, p = 0.03; IOX 0.18 ± 0.21 before vs. 0.46 ± 0.30, p = 0.01 during stimulation). Similarly, when using the SARS implant, we also observed blood perfusion significantly increased (IHB 1.01 ± 0.02 before vs.1.07 ± 0.02 during stimulation, p = 0.003; IOX 0.79 ± 0.81 before vs. 2.2 ± 1.21 during stimulation, p = 0.036). Among four participants who completed both the FMS and FES studies, the magnitude of increase in both parameters was significantly higher during FMS. This study demonstrates sacral nerve root stimulation confer better benefit on blood perfusion than applying traditional FES in SCI population.     

Enhanced sympathetic nervous activity after intravenous propranolol in ischaemic heart disease: plasma noradrenaline splanchnic blood flow and mixed venous oxygen saturation at rest and during exercise

To study the mechanisms by which acute beta-adrenergic blockade may change the activity of the sympathetic nervous system we have measured haemodynamic responses including splanchnic blood flow in twenty-three patients with ischaemic heart disease at rest and during supine exercise before and after i.v. injection of 0.039 mmol (10 mg) dl-propranolol. After propranolol both at rest and on exercise blood pressure, cardiac output and heart rate decreased, while splanchnic vascular resistance increased; mixed venous oxygen saturation decreased whilst arterial oxygen saturation and oxygen uptake were unchanged. Plasma noradrenaline increased after propranolol, values correlating with mixed venous oxygen saturation and splanchnic vascular resistance, both at rest and during exercise before and after propranolol, only at rest was there any correlation with arterial blood pressure. The increase in sympathetic nervous activity after propranolol may be due to a reduction in cardiac output and thereby alteration of the metabolic state (oxygen or related factors) in tissues. Afferent neural signals from the tissues may play a significant role in the regulation of sympathetic nervous activity.     

Effect of pilocarpine on substance P and calcitonin gene‐related peptide releases correlate with salivary secretion in human saliva and plasma

What is known and Objective:  Pilocarpine, a muscarinic receptor agonist, has been used for the treatment of dry mouth. Salivary glands are supplied with nerve fibres that contain neuropeptides, such as substance P, calcitonin gene‐related peptide (CGRP) and vasoactive intestinal polypeptide (VIP), which are important modulators of salivation. It is known that measurement of salivary and plasma levels of neuropeptides is useful for assessing the dose–pharmacological effect relationship of drugs. The relationship between the action of pilocarpine and neuropeptides in humans has not been studied. Moreover, studies evaluate the usefulness of drug salivary levels in the pharmacological evaluation of drugs are scarce. The aim of this study was to examine the effects of pilocarpine on the levels of substance P‐, CGRP‐ and VIP‐like immunoreactive substances (IS) in saliva and plasma taken in healthy humans. Methods:  Five healthy male subjects participated in this study. Pilocarpine tablet (10 mg) or placebo tablet was orally administered with 100 mL of water. Each subject was administered placebo and drug with an interval of 4 weeks in between. Saliva was sampled before and at 20, 40, 60, 90, 120, 180 and 240 min after administration of the test substances. Venous blood samples (10 mL) were also taken from a forearm vein at each time interval. The samples were then enzyme immunoassayed using a highly sensitive system for substance P‐, CGRP‐ and VIP‐IS. The amount of saliva was measured by the Saxon test. Results:  A single oral administration of pilocarpine increased the release of salivary substance P‐IS (the area under the concentration‐time curve: AUC_{0→240 min}) compared with the placebo. Pilocarpine also significantly increased the release of salivary CGRP‐IS (AUC_{0→240 min}). Pilocarpine significantly increased the release of plasma CGRP‐IS. The salivary volume correlated with the salivary level of substance P and CGRP‐IS (r = 0·84, P < 0·05 and r = 0·59, P < 0·05, respectively). AUC_{0→240 min} for substance P‐IS in saliva correlated with that for plasma (r = 0·78, P < 0·05). What is new and Conclusion:  Pilocarpine increases the release of salivary substance P and CGRP‐IS. This suggests that one mechanism by which pilocarpine improves dry mouth is by local stimulation of neuropeptidergic nerves. Moreover, saliva levels of substance P showed good correlation with the plasma levels. The substance P levels in saliva and plasma may be good indicators of the effects of drugs used in dry mouth/xerostomic patients.     

Cardiovascular and adrenergic effects of cigarette smoking during immediate non-selective and selective beta adrenoceptor blockade in humans

The cardiovascular and adrenergic responses to cigarette smoking during acute selective and non-selective beta adrenoceptor blockade were studied in seven young healthy volunteers in a double blind cross-over fashion. Heart rate, arterial blood pressure, forearm blood flow and plasma levels of adrenaline and noradrenaline were determined before and during the terminal 5 min period of 15 min smoking test. During smoking, plasma concentrations of adrenaline increased markedly and evenly by approximately 0.3 ng/ml in all three experimental sessions. Plasma concentrations of noradrenaline remained unchanged. Propranolol, a non-selective beta blocker, caused a marked rise in diastolic and mean blood pressure and forearm vascular resistance during smoking. This response was not seen in the control series or after selective beta-1 blockage with atenolol. This difference is attributable to propranolol's blockade of adrenaline's vasodilating effect mediated by beta-2 receptors in the resistance vessels. Furthermore, atenolol attenuated the systolic blood pressure and tachycardiac responses induced by cigarette smoking by comparison with placebo. This study suggests that selective beta-1 blockers are preferable in the management of patients who are habitual smokers.     

Effect of set configuration on hemodynamics and cardiac autonomic modulation after high‐intensity squat exercise

The aim of this study was to compare the effect of two different high‐intensity resistance exercise (RE) set configurations on the following: systolic blood pressure (SBP), rate pressure product (RPP), heart rate (HR) variability (HRV), and HR complexity (HRC). Ten well‐trained males performed three parallel squat sets until failure (traditional training; TT) with the four repetitions maximum load (4RM), and a rest of 3 min between sets. Thereafter, participants performed a cluster training session (CT) of equated load but with resting time distributed between each repetition. Dependent variables were recorded before, during, and after RE. Mean SBP (25·7 versus 10·9% percentage increase; P = 0·016) and RPP (112·5 versus 69·9%; P = 0·01) were significantly higher in TT. The decrease in HRV after exercise and the drop of HRC during exercise were similar in CT and TT. Change of standard deviation of normal RR intervals after TT correlated with change in SBP (r = 0·803; P = 0·009) while the change of Sample Entropy during exercise correlated with the increment of RPP during CT (ρ = ?0·667; P = 0·05). This study suggests that set configuration influences acute cardiovascular responses during RE. When intensity, volume and work‐to‐rest ratio are equated, CT is less demanding in terms of SBP and RPP. A greater hemodynamic response during exercise would be associated with a faster parasympathetic recovery.     

Heart rate recovery after constant‐load exercise tests is decreased in proportion to the importance (severity and diffusion) of exercise‐induced lower‐limb ischaemia

Background: Conditions that may influence heart rate recovery at 1 min of recovery from exercise (HRR1: end‐exercise heart rate minus heart rate 1 min after exercise) are not fully understood. We hypothesized that the ‘importance’ (both local severity and regional diffusion) of peripheral skeletal muscle ischaemia is associated with low HRR1. Design and Methods: In 529 patients with suspected or confirmed peripheral vascular disease not receiving beta‐blockers (61·4 ± 11·3 years old), we retrospectively studied the relationship of HRR1 to exercise‐induced changes in transcutaneous oxygen DROP index (limb changes minus chest changes from rest). The sum of DROP indices observed on both calves and both buttocks (DROPtot) provides the unique opportunity to estimate both the severity and the diffusion of exercise‐induced ischaemia on the right and left side simultaneously. It was used during a constant‐load treadmill test (3·2 km h^?1; 10% grade) to classify patients in quartiles, the fourth quartile representing the more ‘important’ ischaemias. Results: There was an inverse relationship between quartiles of DROPtot and HRR1, even after adjustment for heart rate reserve (Delta HR: end‐exercise minus resting heart rate), age (≤ or >60 years), gender, body mass index, treadmill maximal walking distance and ankle brachial index: adjusted R = 0·629; P<0·0001. Conclusions: During constant‐load treadmill testing, DROPtot, an index of the ‘importance’ of exercise‐induced lower‐limb ischaemia, correlates with HRR1. Whether HRR1 is improved in proportion of DROPtot improvement in patients undergoing surgery or rehabilitation for peripheral artery disease is a fascinating issue for future studies.     

Simultaneous quantification of myocardial perfusion,oxidative metabolism,cardiac efficiency and pump function at rest and during supine bicycle exercise using 1‐11C‐acetate PET – a pilot study

Background: PET using 1‐¹¹C‐acetate (ACE‐PET) applied at rest is used for measuring absolute myocardial blood flow (MBF) and oxidative metabolic rate (k_mono). We evaluated the feasibility of quantitative ACE‐PET during exercise. Methods: Five endurance athletes underwent dynamic PET scanning at rest and during supine bicycle stress. Exercise was maintained at a workload of 120 Watt for 17 min. The rate‐pressure product (RPP) was recorded repeatedly. MBF, k_mono in left (LV) and right (RV) ventricular wall, cardiac output (CO), cardiac efficiency and a lung uptake value reflecting left heart diastolic pressures were calculated from the PET data using previously validated models. Results: MBF increased from 0·71 ± 0·17 to 2·48 ± 0·25 ml min^?1 per ml, LV‐k_mono from 0·050 ± 0·005 to 0·146 ± 0·021 min^?1, RV‐k_mono from 0·023 + 0·006 to 0·087 + 0·014 min^‐1, RPP from 4·7 ± 0·8 to 13·2 ± 1·4 mmHg × min^?1 × 10³ and Cardiac Output from 5·2 ± 1·1 to 12·3 ± 1·2 l min ^?1 (all P < 0·001). Cardiac efficiency was unchanged (P = 0·99). Lung uptake decreased from 1·1 ± 0·2 to 0·6 ± 0·1 ml g^?1 (P < 0·001). Discussion: A number of important parameters related to cardiac function can be quantified non‐invasively and simultaneously with a short scanning protocol during steady state supine bicycling. This might open up new opportunities for studies of the integrated cardiac physiology in health and early asymptomatic disease.     

Effect of β1-adrenoceptor blockade on plasma levels of atrial natriuretic peptide during exercise in normal man

Summary. Increased plasma levels of atrial natriuretic peptide (ANP) during exercise have been reported. To investigate the role of tachycardia as a stimulus for release of ANP during exercise the following study was undertaken. Graded exercise was performed in six healthy volunteers before and after β₁-adrenoceptor blockade. Plasma levels of ANP were determined at different workloads in both cases. At rest and at all workloads during exercise plasma levels of ANP were higher after β₁-adrenoceptor blockade than without. Therefore, it is unlikely that tachycardia is a major stimulus for secretion of ANP during exercise. It is suggested that increased right atrial pressure and/or pulmonary arterial blood pressure and increased plasma levels of catecholamines are important secretory stimuli for ANP during exercise.     

Circulatory response to single circuit weight and walking training sessions of similar energy cost in middle‐aged overweight females

The aim of this study was to compare circulatory responses to circuit weight (CWT) and aerobic walking training sessions of similar energy cost in middle‐aged overweight females. Thirty‐three middle‐aged pre‐menopausal females participated in the experiment. They were divided into overweight (n=18, 36·2 ± 6·3 years, 166·3 ± 8·0 cm, 83·5 ± 9·7 kg, BMI 30·2 ± 3·1 kg m^–2) and non‐overweight control (n=15, 34·1 ± 6·3 years, 165·0 ± 5·6 cm, 61·6 ± 5·0 kg, BMI 22·7 ± 1·5 kg m^–2) groups. Individual physical working capacity (PWC) was measured using the cycle ergometer test (calculated at the level of predicted HR_max (205 – ½ age). A CWT session consisted of leg extension, bench press, sit‐ups and leg press exercises. The subjects performed four circuits at the maximal possible speed, using a work‐to‐rest ratio of 60 s. Blood pressure (BP) was measured during every rest period between the exercises, and the heart rate (HR) was recorded continuously during the whole CWT programme. During the walking training session, the subjects walked as fast as possible on the indoor track. The total energy cost of the walking training session was the same as during the CWT session, approximately 270 kcal, and was controlled by a CALTRAC accelerometer. HR and BP were measured every 5 min during the walking training session. The PWC index was significantly (P<0·05) higher in the overweight group in comparison with the control females (215·4 ± 76·1 and 187·9 ± 42·4 W, respectively). The resting BP was normal in both groups (<140/90 mmHg). HR was between 120 and 140 beats min^–1 during CWT and walking sessions. There were no differences in BP during both training sessions in overweight and control subjects. It was concluded that both CWT and walking training sessions were acceptable forms of physical activity to increase cardiovascular fitness in middle‐aged overweight and normal body weight females.     

Effects of blood‐flow‐restricted resistance training on muscle function in a 74‐year‐old male with sporadic inclusion body myositis: a case report

Sporadic inclusion body myositis (sIBM) is a systemic disease that is characterized by substantial skeletal muscle weakness and muscle inflammation, leading to impaired physical function. The objective was to investigate the effect of low‐load resistance exercise with concurrent partial blood flow restriction to the working muscles (blood‐flow‐restricted (BFR) training) in a patient with sIBM. The training consisted of 12 weeks of lower extremity BFR training with low training loads (~25‐RM). The patient was tested for mechanical muscle function and functional capacity before and after 6 and 12 weeks of training. Maximal horizontal gait speed increased by 19%, which was accompanied by 38–92% improvements in mechanical muscle function (maximal isometric strength, rate of force development and muscle power). In conclusion, BFR training was well tolerated by the patient with sIBM and led to substantial improvements in mechanical muscle function and gait speed.     

Coronary perfusion pressure during external chest compression in pseudo-EMD, comparison of systolic versus diastolic synchronization

Background

The fraction of cardiac arrest patients presenting with pulseless electrical activity is increasing, and it is likely that many of these patients have pseudo-electromechanical dissociation (P-EMD), a state in which there is residual cardiac contraction without a palpable pulse. The efficacy of cardiopulmonary resuscitation (CPR) with external chest compression synchronized with the P-EMD cardiac systole and diastole has not been fully evaluated.

Hypothesis

During external chest compression in P-EMD, the coronary perfusion pressure (CPP) will be greater with systolic synchronization compared with diastolic phase synchronization.

Methods

A porcine model of P-EMD induced by progressive hypoxia with peak aortic pressures targeted to 50 mmHg was used. CPR chest compressions were performed by either load distributing band or vest devices. Paired 10 s intervals of systolic and diastolic synchronization were performed randomly during P-EMD, and aortic, right atrial and CPP were compared.

Results

Stable P-EMD was achieved in 8 animals, with 2.6 ± 0.5 matched synchronization pairs per animal. Systolic synchronization was association with increases in relaxation phase aortic pressure (41.7 ± 8.9 mmHg vs. 36.9 ± 8.2 mmHg), and coronary perfusion pressure (37.6 ± 11.7 mmHg vs. 30.2 ± 9.6 mmHg). Diastolic synchronization was associated with an increased right atrial pressure (6.7 ± 4.1 mmHg vs. 4.1 ± 5.7 mmHg).

Conclusion

During P-EMD, synchronization of external chest compression with residual cardiac systole was associated with higher CPP compared to synchronization with diastole.