In situ cardiac performance of Atlantic cod (Gadus morhua) at cold temperatures: long-term acclimation, acute thermal challenge and the role of adrenaline

The resting and maximum in situ cardiac performance of Newfoundland Atlantic cod (Gadus morhua) acclimated to 10, 4 and 0°C were measured at their respective acclimation temperatures, and when acutely exposed to temperature changes: i.e. hearts from 10°C fish cooled to 4°C, and hearts from 4°C fish measured at 10 and 0°C. Intrinsic heart rate (f(H)) decreased from 41 beats min(-1) at 10°C to 33 beats min(-1) at 4°C and 25 beats min(-1) at 0°C. However, this degree of thermal dependency was not reflected in maximal cardiac output (Q(max) values were ~44, ~37 and ~34 ml min(-1) kg(-1) at 10, 4 and 0°C, respectively). Further, cardiac scope showed a slight positive compensation between 4 and 0°C (Q(10)=1.7), and full, if not a slight over compensation between 10 and 4°C (Q(10)=0.9). The maximal performance of hearts exposed to an acute decrease in temperature (i.e. from 10 to 4°C and 4 to 0°C) was comparable to that measured for hearts from 4°C- and 0°C-acclimated fish, respectively. In contrast, 4°C-acclimated hearts significantly out-performed 10°C-acclimated hearts when tested at a common temperature of 10°C (in terms of both Q(max) and power output). Only minimal differences in cardiac function were seen between hearts stimulated with basal (5 nmol l(-1)) versus maximal (200 nmol l(-1)) levels of adrenaline, the effects of which were not temperature dependent. These results: (1) show that maximum performance of the isolated cod heart is not compromised by exposure to cold temperatures; and (2) support data from other studies, which show that, in contrast to salmonids, cod cardiac performance/myocardial contractility is not dependent upon humoral adrenergic stimulation.

Noninvasive measurement of cardiac output during exercise by inert gas rebreathing technique

Reduced exercise tolerance and dyspnea during exercise are hallmarks of heart failure syndrome. Exercise capacity and various parameters of cardiopulmonary response to exercise are of important prognostic value. All the available parameters only indirectly reflect left ventricular dysfunction and hemodynamic adaptation to an increased demand. Noninvasive assessment of cardiac output, especially during an incremental exercise stress test, would allow the direct measure of cardiac reserve and may become the gold standard for prognostic evaluation in the future.

Corticospinal output and loss of force during motor fatigue

The objective of this study was to analyze central motor output changes in relation to contraction force during motor fatigue. The triple stimulation technique (TST, Magistris et al. in Brain 121(Pt 3):437-450, 1998) was used to quantify a central conduction index (CCI = amplitude ratio of central conduction response and peripheral nerve response, obtained simultaneously by the TST). The CCI removes effects of peripheral fatigue from the quantification. It allows a quantification of the percentage of the entire target muscle motor unit pool driven to discharge by a transcranial magnetic stimulus. Subjects (n = 23) performed repetitive maximal voluntary contractions (MVC) of abductor digiti minimi (duration 1 s, frequency 0.5 Hz) during 2 min. TST recordings were obtained every 15 s, using stimulation intensities sufficient to stimulate all cortical motor neurons (MNs) leading to the target muscle, and during voluntary contractions of 20% of the MVC to facilitate the responses. TST was also repetitively recorded during recovery. This basic exercise protocol was modified in a number of experiments to further characterize influences on CCI of motor fatigue (4 min exercise at 50% MVC; delayed fatigue recovery during local hemostasis, "stimulated exercise" by 20 Hz trains of 1 s duration at 0.5 Hz during 2 min). In addition, the cortical silent period was measured during the basic exercise protocol. Force fatigued to approximately 40% of MVC in all experiments and in all subjects. In all subjects, CCI decreased during exercise, but this decrease varied markedly between subjects. On average, CCI reductions preceded force reductions during exercise, and CCI recovery preceded force recovery. Exercising at 50% for 4 min reduced muscle force more markedly than CCI. Hemostasis induced by a cuff delayed muscle force recovery, but not CCI recovery. Stimulated exercise reduced force markedly, but CCI decreased only marginally. Summarized, force reduction and reduction of the CCI related poorly quantitatively and in time, and voluntary drive was particularly critical to reduce the CCI. The fatigue induced reduction of CCI may result from a central inhibitory phenomenon. Voluntary muscle activation is critical for the CCI reduction, suggesting a primarily supraspinal mechanism.

The effects of cardiac output and pulmonary arterial hypertension on volumetric capnography derived-variables during normoxia and hypoxia

The aim of this study was to test the effect of cardiac output (CO) and pulmonary artery hypertension (PHT) on volumetric capnography (VCap) derived-variables. Nine pigs were mechanically ventilated using fixed ventilatory settings. Two steps of PHT were induced by IV infusion of a thromboxane analogue: PHT25 [mean pulmonary arterial pressure (MPAP) of 25 mmHg] and PHT40 (MPAP of 40 mmHg). CO was increased by 50 % from baseline (COup) with an infusion of dobutamine ≥5 μg kg(-1) min(-1) and decreased by 40 % from baseline (COdown) infusing sodium nitroglycerine ≥30 μg kg(-1) min(-1) plus esmolol 500 μg kg(-1) min(-1). Another state of PHT and COdown was induced by severe hypoxemia (FiO2 0.07). Invasive hemodynamic data and VCap were recorded and compared before and after each step using a mixed random effects model. Compared to baseline, the normalized slope of phase III (SnIII) increased by 32 % in PHT25 and by 22 % in PHT40. SnIII decreased non-significantly by 4 % with COdown. A combination of PHT and COdown associated with severe hypoxemia increased SnIII by 28 % compared to baseline. The elimination of CO2 per breath decreased by 7 % in PHT40 and by 12 % in COdown but increased only slightly with COup. Dead space variables did not change significantly along the protocol. At constant ventilation and body metabolism, pulmonary artery hypertension and decreases in CO had the biggest effects on the SnIII of the volumetric capnogram and on the elimination of CO2.

Only Neochordoplasty Achieves Physiological Trans-valvular Pressure Gradients After Repair Of Acute Posterior Leaflet Prolapse In Porcine Mitral Valves

Objective: Minimizing resection and preserving leaflet tissue has been previously shown to be beneficial for mitral valve function and leaflet kinematics after repair of acute posterior leaflet prolapse in porcine valves. We examined the effects of different additional methods of mitral valve repair (neochordoplasty, ring annuloplasty, edge-to-edge repair and triangular resection) on hemodynamics at different heart rates in an experimental model. Methods: Severe acute P2 prolapse was created in eight porcine mitral valves by resecting the posterior marginal chordae. Valve hemodynamics was quantified under pulsatile conditions in an in vitro heart simulator before and after surgical manipulation. Mitral regurgitation was corrected using four different methods of repair on the same valve: neochordoplasty with expanded polytetrafluoroethylene sutures alone and together with ring annuloplasty, edge-to-edge repair and triangular resection, both with non-restrictive annuloplasty. Residual mitral valve leak, trans-valvular pressure gradients, flow and cardiac output were measured at 60 and 80 beats/min. A validated statistical linear mixed model was used to analyze the effect of treatment. The p values were calculated using a two-sided Wald test. Results: Only neochordoplasty with expanded polytetrafluoroethylene sutures but without ring annuloplasty achieved similar hemodynamics compared to those of the native mitral valve (p range 0.071-0.901). Trans-valvular diastolic pressure gradients were within a physiologic range but significantly higher than those of the native valve following neochordoplasty with ring annuloplasty (p=0.000), triangular resection (p=0.000) and edge-to-edge repair (p=0.000). Neochordoplasty alone was significantly better in terms of hemodynamic than neochordoplasty with a ring annuloplasty (p=0.000). These values were stable regardless of heart rate or ring size. Conclusions: Neochordoplasty without ring annuloplasty is the only repair technique able to achieve almost native physiological hemodynamics after correction of leaflet prolapse in a porcine experimental model of acute chordal rupture.

Timing of extreme drought modifies reproductive output in semi-natural grassland

Questions Do extreme dry spells in late summer or in spring affect abundance and species composition of the reproductive shoots and the seed rain in the next annual crop? Are drought effects on reproductive shoots related to the rooting depths of species? Location Species-rich semi-natural grassland at Negrentino, Switzerland. Methods In plots under automated rain-out shelters, rainwater was added to simulate normal conditions and compare them with two experimentally effected long dry spells, in late summer (2004) and in the following spring (2005). For 28 plots, numbers of reproductive shoots per species were counted in 1-m2 areas and seed rain was estimated using nine sticky traps of 102 cm2 after dry spells. Results The two extreme dry spells in late summer and spring were similar in length and their probability of recurrence. They independently reduced the subsequent reproductive output of the community, while their seasonal timing modified its species composition. Compared to drought in spring, drought in late summer reduced soil moisture more and reduced the number of reproductive shoots of more species. The negative effects of summer drought decreased with species’ rooting depth. The shallow-rooted graminoids showed a consistent susceptibility to summer drought, while legumes and other forbs showed more varied responses to both droughts. Spring drought strongly reduced density (–53%) and species richness (–43%) of the community seed rain, while summer drought had only a marginally significant impact on seed density of graminoids (–44%). Reductions in seed number per shoot vs reproductive shoot density distinguished the impacts of drought with respect to its seasonal timing. Conclusion The essentially negative impact of drought in different seasons on reproductive output suggests that more frequent dry spells could contribute to local plant diversity loss by aggravating seed deficiency in species-rich grassland.