A pilot study quantifying the shape of tidal breathing waveforms using centroids in health and COPD

During resting tidal breathing the shape of the expiratory airflow waveform differs with age and respiratory disease. While most studies quantifying these changes report time or volume specific metrics, few have concentrated on waveform shape or area parameters. The aim of this study was to derive and compare the centroid co-ordinates (the geometric centre) of inspiratory and expiratory flow-time and flow-volume waveforms collected from participants with or without COPD. The study does not aim to test the diagnostic potential of these metrics as an age matched control group would be required. Twenty-four participants with COPD and thirteen healthy participants who underwent spirometry had their resting tidal breathing recorded. The flow-time data was analysed using a Monte Carlo simulation to derive the inspiratory and expiratory flow-time and flow-volume centroid for each breath. A comparison of airflow waveforms show that in COPD, the breathing rate is faster (17 ± 4 vs 14 ± 3 min(-1)) and the time to reach peak expiratory flow shorter (0.6 ± 0.2 and 1.0 ± 0.4 s). The expiratory flow-time and flow-volume centroid is left-shifted with the increasing asymmetry of the expired airflow pattern induced by airway obstruction. This study shows that the degree of skew in expiratory airflow waveforms can be quantified using centroids.

Estimation of tidal ventilation in preterm and term newborn infants using electromagnetic inductance plethysmography

Tidal volume (VT) measurements in newborn infants remain largely a research tool. Tidal ventilation and breathing pattern were measured using a new device, FloRight, which uses electromagnetic inductive plethysmography,and compared simultaneously with pneumotachography in 43 infants either receiving no respiratory support or continuous positive airway pressure (CPAP).Twenty-three infants were receiving CPAP (gestational age 28 ± 2 weeks, mean ± SD) and 20 were breathing spontaneously (gestational age 34 ± 4 weeks). The two methods were in reasonable agreement, with VT (r2 = 0.69) ranging from 5 to 23 ml (4–11 ml kg−1) with a mean difference of 0.4 ml and limit of agreement of −4.7 to + 5.5 ml. For respiratory rate, minute ventilation,peak flow and breathing pattern indices, the mean difference between the two methods ranged between 0.7% and 5.8%. The facemask increased the respiratory rate (P < 0.001) in both groups with the change in VT being more pronounced in the infants receiving no respiratory support. Thus, FloRight provides an easy to use technique to measure term and preterm infants in the clinical environment without altering the infant's breathing pattern.

A novel clinical method for quantification of regional left ventricular pressure-strain loop area: a non-invasive index of myocardial work

Aims

Left ventricular (LV) pressure–strain loop area reflects regional myocardial work and metabolic demand, but the clinical use of this index is limited by the need for invasive pressure. In this study, we introduce a non-invasive method to measure LV pressure–strain loop area.

Methods and results

Left ventricular pressure was estimated by utilizing the profile of an empiric, normalized reference curve which was adjusted according to the duration of LV isovolumic and ejection phases, as defined by timing of aortic and mitral valve events by echocardiography. Absolute LV systolic pressure was set equal to arterial pressure measured invasively in dogs (n = 12) and non-invasively in patients (n = 18). In six patients, myocardial glucose metabolism was measured by positron emission tomography (PET). First, we studied anaesthetized dogs and observed an excellent correlation (r = 0.96) and a good agreement between estimated LV pressure–strain loop area and loop area by LV micromanometer and sonomicrometry. Secondly, we validated the method in patients with various cardiac disorders, including LV dyssynchrony, and confirmed an excellent correlation (r = 0.99) and a good agreement between pressure–strain loop areas using non-invasive and invasive LV pressure. Non-invasive pressure–strain loop area reflected work when incorporating changes in local LV geometry (r = 0.97) and showed a strong correlation with regional myocardial glucose metabolism by PET (r = 0.81).

Conclusions

The novel non-invasive method for regional LV pressure–strain loop area corresponded well with invasive measurements and with directly measured myocardial work and it reflected myocardial metabolism. This method for assessment of regional work may be of clinical interest for several patients groups, including LV dyssynchrony and ischaemia.

Predicting cardiotoxicity propensity of the novel iodinated contrast medium GE-145: Ventricular fibrillation during left coronary arteriography in pigs

BACKGROUND

Severe side effects caused by iodinated radiographic contrast media (CM) are rare, but can occur in high risk patients and during percutaneous coronary intervention. To minimize this risk a new nonionic CM with low inherent osmolality has been designed, giving room for a relatively high concentration of favorable electrolytes in the isotonic formulation.

PURPOSE

To test a new radiographic CM (GE-145) in a pig model of cardiotoxicity by comparing its ventricular fibrillation (VF) propensity and hemodynamic effects to that of iodixanol.

MATERIAL AND METHODS

Test agents were injected into the left anterior descending coronary artery (LAD) of pigs through an inflated balloon catheter (injection volume 25 ml, injection rate 0.4 ml/s, maximum injection time 62.5 s). Series 1: GE-145 (338 mg I/ml) + 45 mM NaCl and iodixanol (321 mg I/ml) + 19 mM NaCl were injected in five pigs. Series 2: GE-145 (320 mg I/ml) + 45 mM NaCl + 0.1, 0.3, or 0.7 mM CaCl₂ and iodixanol (320 mg I/ml) + 19 mM NaCl + 0.3 mM CaC₂ (Visipaque) were injected in six pigs.

RESULTS

Iodixanol + NaCl caused VF in 6 of 13 injections (46%) after 60.3±7.5 s (mean ± SD). GE-145 + NaCl did not cause any VF in 13 injections (0%) (P<0.05). Iodixanol + 19 mM NaCl + 0.3 mM CaCl₂ caused VF in 9 of 9 injections (100%) after 61±4 s. GE-145 + 45 mM NaCl + 0.1, 0.3, or 0.7 mM CaCl₂ did not cause any VF during or after 9 injections of each agent (0%) (P<0.05). The least hemodynamic effects were seen with GE-145 + 45 mM NaCl + 0.7 mM CaCl₂.

CONCLUSION

In this model of direct administration of CM into the LAD of anesthetized pigs, the tested GE-145 formulations had a significantly lower propensity to induce VF than iodixanol with electrolytes. Favorable hemodynamic properties of GE-145 can be achieved by optimizing concentrations of sodium and calcium.

Reduced release of vasoconstrictors from the porcine heart after repeated periods of ischemia

OBJECTIVE

To examine if the decline in post-ischemic hyperemic flow after repeated brief periods of myocardial ischemia is accompanied by augmented cardiac release of the vasoconstrictors endothelin-1 (ET-1) and norepinephrine (NE).

DESIGN

Mid-LAD (left anterior descending coronary artery) was occluded for 10 min with 30 min intervals a total of four times in six anesthetized pigs. Blood from the anterior interventricular coronary vein was drained through a shunt to the right atrium to facilitate blood sampling. Plasma concentrations of ET-1 and NE were repeatedly measured in arterial and coronary venous blood to estimate cardiac vasoconstrictor release.

RESULTS

Plasma concentrations of ET-1 and NE remained unaltered, but cardiac release of both vasoconstrictors rose briefly during reperfusion due to the hyperemia. However, release declined progressively after repeated periods of ischemia and reperfusion and amounted to 53% (NE) and 17% (ET-1) of initial release after the fourth period of ischemia.

CONCLUSION

The decline in post-ischemic hyperemia after repeated brief periods of myocardial ischemia is not accompanied by a progressive accentuation of cardiac ET-1 and NE release.

Prevalence of raised Yersinia enterocolitica antibody titre in unselected, adult populations in Denmark during 12 years

Yersinia enterocolitica biotype 4, serotype 0:3 is by far the most common human pathogenic Yersinia enterocolitica subtype in Scandinavia. It is extraordinarily immunologically specific, and an elevated antibody titre greater than or equal 80-160 is known to indicate acute infection. This titre was measured in five population surveys conducted in 1967-78, including 3278 examined adult men and women. The prevalence of titre elevation greater than or equal to was 1.0% in 1967. In 1978 it was significantly higher, 7.7%, and also the individual course of the titre in a ten-year longitudinal survey showed a significant increase in this prevalence, indicating an increasing incidence of infection. Significant sex and age differences were seen, women and younger subjects being more frequently affected than men and older subjects. The prevalence of elevated titre showed a seasonal variation with a maximum in the spring and autumn.

Ventricular fibrillation induced by ischemia-reperfusion is not prevented by the NPY Y2 receptor antagonist BIIE0246

Neuropeptide Y is released together with norepinephrine from sympathetic nerve terminals during conditions of increased sympathetic activity. Neuropeptide Y is known to inhibit vagal activity, and accordingly, it might increase the risk for ventricular fibrillation during myocardial ischemia-reperfusion, with concomitant sympathetic stimulation. Counteracting the inhibiting effect of neuropeptide Y by the specific neuropeptide Y2 antagonist, BIIE0246, we expected occurrence of ventricular fibrillation in association with repeated periods of myocardial ischemia-reperfusion to decrease. The midleft anterior descending coronary artery was repeatedly occluded in 16 open-chest pigs. Eight pigs received BIIE0246, and the controls received the vehicle only. Ventricular fibrillation developed in 2 animals of the control group, but in 4 pigs receiving BIIE0246. Occurrence of ventricular fibrillation and ventricular tachycardia did not differ significantly between the 2 groups, and in association with repeated periods of regional myocardial ischemia, did not decline in pigs treated by the specific neuropeptide Y2-receptor antagonist BIIE0246.

Cardiac accumulation of bone marrow mononuclear progenitor cells after intracoronary or intravenous injection in pigs subjected to acute myocardial infarction with subsequent reperfusion

OBJECTIVE

The purpose of the present study was to compare the efficacy of intracoronary and intravenous injection of autologous progenitor cells for homing to the acutely infarcted but reperfused myocardium in pigs.

METHODS

Myocardial infarction was induced in 11 anesthetized pigs by 60-min balloon inflation in the mid LAD. After balloon deflation, reperfusion was verified and autologous CD31(+) progenitor cells, or bone marrow mononuclear cells, labeled with PKH67, were injected either intracoronarily (n=6) or intravenously (n=3). By autopsy, 4-5 days after induction of infarction, tissue from the heart and other organs was obtained for fluorescence microscopy.

RESULTS

In the heart, PKH(+) cells were detected throughout the reperfused infarcted myocardium, and the number of PKH(+) cells was significantly higher after intracoronary than after intravenous injection (3.2+/-0.55 vs. 0.33+/-0.17 cells/high-power field/10(6) cells injected, P=.01). Few PKH(+) cells were detected in the spleen, lung, mesenteric lymph node, and bone marrow. In an additional animal with a coil placed in the mid LAD, progenitor cells were not detected in the infarcted myocardium or in the normal myocardium.

CONCLUSION

Autologous mononuclear and CD31(+) cells from bone marrow accumulated in the infarcted myocardium when injected intracoronarily or intravenously after established reperfusion, and the accumulation of cells was significantly greater after intracoronary injection than after intravenous injection. Accumulation of PKH(+) cells did not appear in the normal myocardium or in the nonreperfused infarcted myocardium. PKH(+) cells were detected in spleen, lung, and bone marrow but to a lesser degree than in the infarcted myocardium.

Haemodynamic effects of adrenaline (epinephrine) depend on chest compression quality during cardiopulmonary resuscitation in pigs

BACKGROUND

Adrenaline (epinephrine) is used during cardiopulmonary resuscitation (CPR) based on animal experiments without supportive clinical data. Clinically CPR was reported recently to have much poorer quality than expected from international guidelines and what is generally done in laboratory experiments. We have studied the haemodynamic effects of adrenaline during CPR with good laboratory quality and with quality simulating clinical findings and the feasibility of monitoring these effects through VF waveform analysis.

METHODS AND RESULTS

After 4 min of cardiac arrest, followed by 4 min of basic life support, 14 pigs were randomised to ClinicalCPR (intermittent manual chest compressions, compression-to-ventilation ratio 15:2, compression depth 30-38 mm) or LabCPR (continuous mechanical chest compressions, 12 ventilations/min, compression depth 45 mm). Adrenaline 0.02 mg/kg was administered 30 s thereafter. Plasma adrenaline concentration peaked earlier with LabCPR than with ClinicalCPR, median (range), 90 (30, 150) versus 150 (90, 270) s (p = 0.007), respectively. Coronary perfusion pressure (CPP) and cortical cerebral blood flow (CCBF) increased and femoral blood flow (FBF) decreased after adrenaline during LabCPR (mean differences (95% CI) CPP 17 (6, 29) mmHg (p = 0.01), FBF -5.0 (-8.8, -1.2) ml min(-1) (p = 0.02) and median difference CCBF 12% of baseline (p = 0.04)). There were no significant effects during ClinicalCPR (mean differences (95% CI) CPP 4.7 (-3.2, 13) mmHg (p = 0.2), FBF -0.2 (-4.6, 4.2) ml min(-1)(p = 0.9) and CCBF 3.6 (-1.8, 9.0)% of baseline (p = 0.15)). Slope VF waveform analysis reflected changes in CPP.

CONCLUSION

Adrenaline improved haemodynamics during laboratory quality CPR in pigs, but not with quality simulating clinically reported CPR performance.

The influence of a one-step reamer-irrigator-aspirator technique on the intramedullary pressure in the pig femur

BACKGROUND

Increased intramedullary pressure in the femoral cavity causes intravasation of bone marrow content to the circulation which may lead to occlusion of pulmonary vessels and cardiorespiratory dysfunction. A one-step reamer-irrigator-aspirator (RIA) technique has been developed to reduce the intramedullary pressure (IMP) during the reaming procedure. This study was design to compare IMP with a standard reaming technique with IMP during reaming with the RIA system with a hypothesis that the RIA system would involve lower pressures.

MATERIAL AND METHOD

In a randomised study in 19 Norwegian landrace pigs reamed intramedullary nailing was performed with two different reamer devices. Nine animals were operated with a traditional reamer and 10 animals with RIA. One animal in the RIA group was excluded due to a perioperative femoral fracture, and three animals in the traditional group were excluded due to a perforation of the distal medial femoral cortex. The intramedullary pressure was registrated with a transducer-tipped pressure monitoring catheter during reaming.

RESULTS

There was a significantly higher intramedullary pressure (P<0.05) during reaming in the traditional reamer group (mean 188+/-38 mmHg) than in the RIA group (mean 33+/-8 mmHg). Intramedullary pressures recorded before surgery, at the opening of the femoral cavity with an awl, by insertion of a guide wire, at insertion of the intramedullary nail, and 10 min after nail insertion showed no significant differences between the groups.

CONCLUSION

The use of a one-step reamer-irrigator-aspirator technique in the pig femur induced less intramedullary pressure increase than the use of a traditional reamer.

Cardiac fibrinolytic capacity is markedly increased after brief periods of local myocardial ischemia, but declines following successive periods in anesthetized pigs

BACKGROUND

Fibrinolysis in blood is mainly reflected by the activities of tissue plasminogen activator (tPA) and of plasminogen activator inhibitor-1 (PAI-1). The effect of myocardial ischemia on their activities in the coronary circulation is, however, not established.

OBJECTIVES

With an improved experimental model, we therefore examined the effect of a brief period of myocardial ischemia on their activities. Furthermore, the consequences of repeated periods of ischemia, mimicking the situations in patients with unstable angina, were investigated.

METHODS

In six anesthetized pigs, we occluded the distal left anterior descending coronary artery (LAD) four times for 10 min with 40 min intervals and determined the activities of tPA and PAI-1 in arterial and coronary venous blood. By simultaneously recording LAD flow, we could estimate cardiac release of these factors at baseline conditions and during reperfusion.

RESULTS

Neither net cardiac release of PAI-1 nor alterations in plasma PAI-1 levels were demonstrated during the experiment. However, a significant net release of tPA activity of 10.4 +/- 3.2 IU mL(-1) (P < 0.005) was recorded during baseline conditions. During reperfusion following the first period of ischemia, the cardiac release of tPA activity increased to a peak of 103 +/- 30-fold baseline release, but declined progressively after repeated periods of ischemia. After the fourth period, tPA release did not exceed an estimated baseline accumulation during ischemia and early reperfusion.

CONCLUSIONS

In this porcine model, a substantial local increase in fibrinolytic capacity was observed after brief periods of ischemia, but declined subsequently by repeated periods of ischemia.

Oxygen delivery and return of spontaneous circulation with ventilation:compression ratio 2:30 versus chest compressions only CPR in pigs

The need for rescue breathing during the initial management of sudden cardiac arrest is currently being debated and reevaluated. The present study was designed to compare cerebral oxygen delivery during basic life support (BLS) by chest compressions only with chest compressions plus ventilation in pigs with an obstructed airway mimicked by a valve hindering passive inhalation. Resuscitability was then studied during the subsequent advanced life support (ALS) period. After 3 min of untreated ventricular fibrillation (VF) BLS was started. The animals were randomised into two groups. One group received chest compressions only. The other group received ventilations and chest compressions with a ratio of 2:30. A gas mixture of 17% oxygen and 4% carbon dioxide was used for ventilation during BLS. After 10 min of BLS, ALS was provided. All six pigs ventilated during BLS attained a return of spontaneous circulation (ROSC) within the first 2 min of advanced cardiopulmonary resuscitation (CPR) compared with only one of six compressions-only pigs. While all except one compressions-only animal achieved ROSC before the experiment was terminated, the median time to ROSC was shorter in the ventilated group. With a ventilation:compression ratio of 2:30 the arterial oxygen content stayed at 2/3 of normal, but with compressions-only, the arterial blood was virtually desaturated with no arterio-venous oxygen difference within 1.5-2 min. Haemodynamic data did not differ between the groups. In this model of very ideal BLS, ventilation improved arterial oxygenation and the median time to ROSC was shorter. We believe that in cardiac arrest with an obstructed airway, pulmonary ventilation should still be strongly recommended.

Increased spillover of norepinephrine to the portal vein during CO-pneumoperitoneum in pigs

BACKGROUND

Elevated intra abdominal pressure (IAP) during CO2-insufflation has been associated with increased catecholamine concentrations in plasma. We have previously indicated that this may be due to a regional increased spillover from the abdominal region. In this experimental study we investigated catecholamine spillover from the drainage area of the portal vein during CO2-pneumoperitoneum.

METHODS

Eight pigs under general anesthesia were investigated before and after CO2-pneumoperitoneum with an IAP of 15 mmHg. Regional spillover of catecholamines was determined by measuring plasma catecholamine concentrations and flow simultaneously. Plasma concentrations of catecholamines were measured from the portal and femoral veins, the pulmonary and carotid arteries. Flow data were collected with laser-Doppler transit time flow probes around the portal and femoral veins. Cardiac output was measured by the thermo-dilution technique. Estimated spillover was calculated by the veno-arterial difference multiplied by flow.

RESULTS

We found a significant increase in estimated spillover of norepinephrine from the drainage area of the portal vein from 10 (-1.2, 78) ng x min(-1) to 27 (1.8, 475) ng x min(-1)[median (range)] (P = 0.05), but no change in estimated spillover of norepinephrine from the drainage area of the femoral vein. Plasma concentrations of norepinephrine increased in central venous and arterial blood. There was no significant change in epinephrine concentrations in arterial blood.

CONCLUSION

Estimated norepinephrine spillover from the drainage area of the portal vein increased during CO2-pneumoperitoneum in pigs. This may indicate that the increased norepinephrine concentrations found in arterial plasma reflects a local activation of sympathetic nerves in the region of the portal drainage area.

Beat-to-beat noninvasive stroke volume from arterial pressure and Doppler ultrasound

The proper understanding of the cardiovascular mechanisms involved in complaints of short-lasting dizziness and the evaluation of unexplained recurrent syncope requires continuous monitoring of cardiac stroke volume (SV) in addition to blood pressure and heart rate. The primary aim of the present study was to evaluate a pulse wave analysis method that calculates beat-to-beat flow from non-invasive arterial pressure by simulating a non-linear, time-varying model of human aortic input impedance (Modelflow; MF), by comparing MF stroke volume (SV(MF)) to Doppler ultrasound (US) flow velocity SV (SV(US)). A second purpose was to compare the two methods under two different conditions: the supine and head-up tilt (30 degrees ) position. SV(US) and SV(MF) with non-invasive arterial pressure (Finapres) as input to the aortic model were measured beat-to-beat during spontaneous supine breathing and in the passive 30 degrees head-up tilt (HUT30) position in six normotensive healthy humans [three females, mean age 24 (21-26) years]. There were variations in supine SV track between the two methods with zero difference and a SD of the beat-to-beat difference (MF-US) of 4.2%. HUT30 induced a systematic difference of 10.5% and an increase in SD to 6.9%, which was reproducible. Beat-to-beat changes in SV in the supine resting condition were equally well assessed by both methods. Systematic differences appear during HUT30 and show opposite signs. The difference between the two methods upon a change in body position may be attributed to limitations in each method.

Quality of CPR with three different ventilation:compression ratios

Current adult basic cardiopulmonary resuscitation (CPR) guidelines recommend a 2:15 ventilation:compression ratio, while the optimal ratio is unknown. This study was designed to compare arterial and mixed venous blood gas changes and cerebral circulation and oxygen delivery with ventilation:compression ratios of 2:15, 2:50 and 5:50 in a model of basic CPR. Ventricular fibrillation (VF) was induced in 12 anaesthetised pigs, and satisfactory recordings were obtained from 9 of them. A non-intervention interval of 3 min was followed by CPR with pauses in compressions for ventilation with 17% oxygen and 4% carbon dioxide in a randomised, cross-over design with each method being used for 5 min. Pulmonary gas exchange was clearly superior with a ventilation:compression ratio of 2:15. While the arterial oxygen saturation stayed above 80% throughout CPR for 2:15, it dropped below 40% during part of the ventilation:compression cycle for both the other two ratios. On the other hand, the ratio 2:50 produced 30% more chest compressions per minute than either of the two other methods. This resulted in a mean carotid flow that was significantly higher with the ratio of 2:50 than with 5:50 while 2:15 was not significantly different from either. The mean cerebrocortical microcirculation was approximately 37% of pre-VF levels during compression cycles alone with no significant differences between the methods. The oxygen delivery to the brain was higher for the ratio of 2:15 than for either 5:50 or 2:50. In parallel the central venous oxygenation, which gives some indication of tissue oxygenation, was higher for the ratio of 2:15 than for both 5:50 and 2:50. As the compressions were done with a mechanical device with only 2-3 s pauses per ventilation, the data cannot be extrapolated to laypersons who have great variations in quality of CPR. However, it might seem reasonable to suggest that basic CPR by professionals should continue with ratio of 2:15 at present if it can be shown that similar brief pauses for ventilation can be achieved in clinical practice.

Pediatric excretory MR urography: comparative study of enhanced and non-enhanced techniques

Our purpose was to compare the quality of ureteral imaging in pediatric patients using two different MR sequences: the non-enhanced heavily T2-weighted (W) turbo spin-echo sequence (TSE) and the gadolinium-enhanced T1W fast-field-echo sequence (T1 FFE). An experimental study on three pigs was first performed. The TSE, before and after furosemide injection, was followed by the T1 FFE sequence. The clinical study included 11 infants and 10 children. With some modifications the same MR parameters and techniques were used as in the animal study. The TSE with TR 8000 ms and TE 650 ms implied 6 radial stacks each of 40 mm thickness. The T1 FFE included TR 18 ms, TE 2.9 ms, flip angle 60, and 50 slices with thickness 0.7 mm. After post-processing, image reconstructions qualitative and quantitative analysis were performed. Complete visualization of the ureters was achieved in 35 of 42 (83%) cases. Seventy-four percent of the ureters were completely visualized with T1 FFE compared with only 19% with TSE. Sixty-nine percent of the ureters were better imaged with T1 FFE than TSE and 21% equally well imaged. Four ureters (10%), either obstructed or due to poor renal function, were better imaged with TSE. The two sequences are complementary. Visualization of non-obstructed ureters is excellent with T1 FFE and the sequence is superior to TSE. The TSE, however, may be equal to or even better than T1 FFE in visualizing obstructed ureters or ureters draining malfunctioning kidneys.

Contractile properties of in situ perfused skeletal muscles from rats with congestive heart failure

We hypothesized that in congestive heart failure (CHF) slow-twitch but not fast-twitch muscles exhibit decreased fatigue resistance in the sense of accelerated reduction of muscle force during activity. Experiments were carried out on anaesthetized rats 6 weeks after induction of myocardial infarction or a sham operation (Sham). Animals with left ventricular end-diastolic pressure (LVEDP) > 15 mmHg under anaesthesia were selected for the CHF group. There was no muscle atrophy in CHF. Force generation by in situ perfused soleus (Sol) or extensor digitorum longus (EDL) muscles was recorded during stimulation (trains at 5 Hz for 6 s (Sol) or 10 Hz for 1.5 s (EDL) at 10 or 2.5 s intervals, respectively) for 1 h in Sol and 10 min in EDL at 37 degrees C. Initial force was almost the same in Sol from CHF and Sham rats, but relaxation was slower in CHF. Relaxation times (95-5 % of peak force) were 177 +/- 55 and 131 +/- 44 ms in CHF and Sham, respectively, following the first stimulation train. After 2 min of stimulation the muscles transiently became slower and maximum relaxation times were 264 +/- 71 and 220 +/- 45 ms in CHF and Sham, respectively (P < 0.05). After 60 min they recovered to 204 +/- 60 and 122 +/- 55 ms in CHF and Sham, respectively (P < 0.05). In CHF but not in Sham rats the force of contraction of Sol declined from the second to the sixtieth minute to 70 % of peak force. The EDL of both CHF and Sham fatigued to 24-28 % of initial force, but no differences in contractility pattern were detected. Thus, slow-twitch muscle is severely affected in CHF by slower than normal relaxation and significantly reduced fatigue resistance, which may explain the sensation of both muscle stiffness and fatigue in CHF patients.

Circulatory responses to a meal in patients with a newly transplanted heart

It is well established that consumption of a meal releases a gradually developing and quite marked increase in blood flow to the gastrointestinal organs and a similar and simultaneous increase in cardiac output (CO). It is not known through which mechanism the pumping of the heart adjusts so accurately to the gastrointestinal flow increase. We have approached this problem by serving a standardized, mixed meal to five patients with recently transplanted and thus denervated hearts and to five sex- and age-matched controls. Pre- and postprandial levels of CO and blood flow in the superior mesenteric artery (SMA) were recorded with Doppler ultrasound technique. The patients with transplanted hearts had significantly higher preprandial levels of heart rate (HR) and CO than the controls. With a timing similar to that seen in the controls did all five patients develop considerable and synchronous postprandial increases in superior mesenteric arterial flow and in CO. Increases in superior mesenteric arterial flow were significantly greater than the controls. Also, COs, high even before meals were given, increased further and to the same relative extent as in the control persons. The marked postprandial increase in CO, probably secondary to the increase in intestinal blood flow, could hardly come about through any sort of nervous reflex to the recently transplanted and denervated hearts. It appears more likely that a humoral connection of some sort exists between the two circulatory events.

Muscle contractile properties during intermittent nontetanic stimulation in rat skeletal muscle

To examine changes in contractile properties and mechanisms of fatigue during submaximal nontetanic skeletal muscle activity, in situ perfused soleus (60-min protocol) and extensor digitorum longus (EDL; 10-min protocol) muscles of the rat were electrically stimulated intermittently at low frequency. The partly fused trains of contractions showed a two-phase change in appearance. During the first phase, relaxation slowed, one-half relaxation time increased, and maximal relaxation first derivative of force (dF/dt) decreased. Developed force during the trains was reduced and was closely related to the rate of relaxation in this first phase. During the second phase, relaxation became faster again, one-half relaxation time decreased, and force returned to resting levels between contractions in a train. In contrast, developed force remained reduced, so that peak force of the contractions was 51% (soleus) and 30% (EDL) of control. In the soleus muscle, the changes in contractile properties were not related to ATP, creatine phosphate, or lactate content. The changes in contractile properties fit best with a mechanism of fatigue involving changes in Ca(2+) handling by the sarcoplasmic reticulum.