Diaphragmatic motor cortex hyperexcitability in patients with chronic obstructive pulmonary disease

Background and objectives

Respiratory muscles dysfunction has been reported in COPD. Transcranial magnetic stimulation (TMS) has been used for assessing the respiratory corticospinal pathways particularly of diaphragm. We aimed to study the cortico-diaphragmatic motor system changes in COPD using TMS and to correlate the findings with the pulmonary function.

Methods

A case control study recruited 30 stable COPD from the out-patient respiratory clinic of Main Alexandria University hospital- Egypt and 17 healthy control subjects who were subjected to spirometry. Cortical conduction of the diaphragm was performed by TMS to all participants followed by cervical magnetic stimulation of the phrenic nerve roots. Diaphragmatic resting motor threshold (DRMT), cortical motor evoked potential latency (CMEPL), CMEP amplitude (CMEPA), peripheral motor evoked potential latency (PMEPL), PMEP amplitude (PMEPA) and central motor conduction time (CMCT) were measured.

Results

66.7% of COPD patients had severe and very severe COPD with median age of 59 (55–63) years. There was statistically significant bilateral decrease in DRMT, CMEPA and PMEPA in COPD group versus healthy subjects and significant increase in CMEPL and PMEPL (p <0.01). Left CMCT was significantly prolonged in COPD group versus healthy subjects (p <0.0001) but not right CMCT. Further, there was significant increase in CMEPL and CMCT of left versus right diaphragm in COPD group (p = 0.003 and 0.001 respectively) that inversely correlated with FEV₁% and FVC% predicted. Right and left DRMT were insignificantly different in COPD group (p >0.05) but positively correlated with FEV₁/FVC, FEV₁% and FVC% predicted.

Conclusion

Central cortico-diaphragmatic motor system is affected in COPD patients with heterogeneity of both sides that is correlated with pulmonary function.

Significance

Coticospinal pathway affection could be a factor for development of diaphragmatic dysfunction in COPD patients accordingly its evaluation could help in personalization of COPD management especially pulmonary rehabilitation programs.

VMAT-SBRT planning based on an average intensity projection for lung tumors located in close proximity to the diaphragm: a phantom and clinical validity study

The aim of the this study was to validate the use of an average intensity projection (AIP) for volumetric-modulated arc therapy for stereotactic body radiation therapy (VMAT-SBRT) planning for a moving lung tumor located near the diaphragm. VMAT-SBRT plans were created using AIPs reconstructed from 10 phases of 4DCT images that were acquired with a target phantom moving with amplitudes of 5, 10, 20 and 30 mm. To generate a 4D dose distribution, the static dose for each phase was recalculated and the doses were accumulated by using the phantom position known for each phase. For 10 patients with lung tumors, a deformable registration was used to generate 4D dose distributions. Doses to the target volume obtained from the AIP plan and the 4D plan were compared, as were the doses obtained from each plan to the organs at risk (OARs). In both phantom and clinical study, dose discrepancies for all parameters of the dose volume (D(min), D(99), D(max), D(1) and D(mean)) to the target were <3%. The discrepancies of D(max) for spinal cord, esophagus and heart were <1 Gy, and the discrepancy of V20 for lung tissue was <1%. However, for OARs with large respiratory motion, the discrepancy of the D(max) was as much as 9.6 Gy for liver and 5.7 Gy for stomach. Thus, AIP is clinically acceptable as a planning CT image for predicting 4D dose, but doses to the OARs with large respiratory motion were underestimated with the AIP approach.

Minimising critical organ irradiation in limited stage Hodgkin lymphoma: a dosimetric study of the benefit of involved node radiotherapy

BACKGROUND

Chemotherapy plus radiotherapy is the standard of care for patients with limited stage Hodgkin lymphoma (HL). Radiotherapy is evolving from involved field radiotherapy (IFRT) to involved node radiotherapy (INRT) to decrease radiotherapy-related morbidity. In the absence of long-term toxicity data, dose-volume metrics of organs at risk (OAR) provide a surrogate measure of toxicity risk.

PATIENTS AND METHODS

Ten female patients with stage I-IIA supradiaphragmatic HL were randomly selected. All patients had pre-chemotherapy computerised tomography (CT) and CT-positron emission tomography staging. Using CT planning, three radiotherapy plans were produced per patient: (i) IFRT, (ii) INRT using parallel-opposed beams and (iii) INRT using volumetric modulated arc therapy (VMAT). Radiotherapy dose was 30.6 Gy in 1.8 Gy fractions. OAR evaluated were lungs, breasts, thyroid, heart and coronary arteries.

RESULTS

Compared with IFRT, INRT significantly reduced mean doses to lungs (P < 0.01), breasts (P < 0.01), thyroid (P < 0.01) and heart (P < 0.01), on Wilcoxon testing. Compared with conventional INRT, VMAT improved dose conformality but increased low-dose radiation exposure to lungs and breasts. VMAT reduced the heart volume receiving 30 Gy (V30) by 85%.

CONCLUSIONS

Reduction from IFRT to INRT decreased the volumes of lungs, breasts and thyroid receiving high-dose radiation, suggesting the potential to reduce long-term second malignancy risks. VMAT may be useful for patients with pre-existing heart disease by minimising further cardiac toxicity risks.

[Study of transcranial magnetic stimulation on diaphragm in patients with obstructive sleep apnea-hypopnea syndrome]

OBJECTIVE

To investigate the changes and possible mechanisms of diaphragm motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS) in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS).

METHODS

Sixteen healthy volunteers (control group), 7 primary snorers (snore group), 13 mild-moderate OSAHS patients (mild-moderate group) and 16 severe OSAHS patients (severe group) were recruited for the study from June in 2005 to June in 2006. Esophageal electrodes combined with TMS and cervical magnetic stimulation (CMS) were used to measure the latency and amplitude of right diaphragm MEP, as well as central motor conduction time (CMCT). The study was repeated in 5 OSAHS patients after effective nasal continuous positive airway pressure (nCPAP) treatment for at least 2 months.

RESULTS

The amplitude of right MEP in severe OSAHS group was (152 +/- 116) microV, which was significantly lower than that in the control group (414 +/- 201) microV, the snore group (352 +/- 99) microV and the mild-moderate group (372 +/- 206) microV. The latency and CMCT in the severe OSAHS group were (18.1 +/- 1.8), (10.6 +/- 1.8) ms respectively, which were significantly longer than those in the control group (13.9 +/- 1.6), (7.7 +/- 1.7) ms, the snore group (14.6 +/- 1.6), (8.1 +/- 1.6) ms, and the mild-moderate group (15.4 +/- 2.7) , (9.0 +/- 2.2) ms. The latency and amplitude of diaphragm MEP as well as CMCT correlated significantly with arousal index, longest apnea duration, minimum pulse oxygen saturation (SpO2), oxygen desaturation index, the percentage of total sleep time with SpO2 below 90% and apnea-hypoxia index (AHI). The latency became significantly shorter after effective nCPAP treatment for more than 2 months, which was (17.5 +/- 0.6) and (15.5 +/- 0.7) ms respectively.

CONCLUSIONS

The latency of MEP and CMCT in OSAHS patients prolonged significantly, while the amplitude of MEP lowered, which may be due to repeated hypoxia, carbon dioxide retention and disorder of sleep structure at night.

Microstimulators and intramuscular hook electrodes for the stimulation of respiratory muscles

BACKGROUND/OBJECTIVES

We determined the feasibility of stimulating the major muscles of respiration with different types of electrodes. Intramuscular hook electrodes, model microstimulators (M-Micro) developed in our laboratory, and commercial radiofrequency microstimulators (RFM) (Alfred Mann Foundation, Valencia, CA), were employed in this investigation.

METHODS

In 8 anesthetized dogs, M-Micro were placed bilaterally on the diaphragm and in the abdominal muscles, and hook electrodes were placed in the 3rd and 5th intercostal regions adjacent to the intercostal nerves known to support inspiration. In 3 of the 8 animals, RFMs (Alfred Mann Foundation) in addition to the M-Micros were sutured to each hemidiaphragm at the same optimal site for phrenic nerve stimulation. During a hyperventilation-induced apnea, 2-second stimulations were applied to the diaphragm and with various combinations of diaphragm plus supporting muscles, both thoracic and abdominal.

RESULTS

Diaphragm stimulation alone provided tidal volumes adequate for basal alveolar ventilation. However, implantation of the RFM required greater contact with the muscle. Stimulating other respiratory muscles along with the diaphragm further increased tidal volumes. The hook electrodes, M-Micro, and RFM performed equally well.

CONCLUSIONS

In the acute dog model, M-Micro and hook electrodes can provide an implant system for the maintenance of ventilation. Support of the intercostal and abdominal muscles has the potential to reduce the contraction requirements of the diaphragm with decreased likelihood of diaphragm fatigue and hypoventilation. Whether the electrodes under investigation could provide an implant system for long-term ventilation needs to be determined.

Vagal pulmonary afferents and central respiratory effects of 5-HT in newborn rats

In decerebrate newborn rats, serotonin (5-HT) is a respiratory depressant via activation of 5-HT2 receptors, whereas it evokes respiratory stimulant effects when applied to the isolated brainstem obtained from the newborn rat. This discrepancy could be due to deafferentation in the in vitro preparation. The aim of our study was to analyse the role of vagal afferents in the modulation of central respiratory effects of 5-HT. In decerebrate cervically or abdominally bivagotomized newborn rats aged between 0 and 3 days, we recorded electrical activity from the diaphragm and from a hypoglossally innervated tongue muscle, as well as cardiac frequency (Fc), before and after application of 5-HT to the floor of the IVth ventricle. The effects of related agents (a 5-HT1A agonist, 8-OH DPAT, and a 5-HT2 agonist, DOI) were studied in cervically bivagotomized animals. For comparison, and to assess the spontaneous variability in inspiratory frequency (Fi) and Fc, sham groups were studied. Each group comprised ten newborn rats. In cervically bivagotomized newborn rats, 5-HT induces a significant increase in Fi, which is the opposite to that observed in decerebrate newborn rats with intact vagi. This respiratory effect is mediated in particular, via activation of 5-HT1A. By contrast, in abdominally bivagotomized newborn rats, a decrease in Fi was observed in response to 5-HT (as previously described in decerebrate animals with intact vagi). We conclude that pulmonary vagal afferents modulate the central respiratory action of 5-HT in decerebrate newborn rats, explaining the conflicting results between in vivo and in vitro experiments.

[Measurement of diaphragm compound muscle action potential with magnetic stimulation of the phrenic nerve and multipara esophageal electrode in intensive care unit]

OBJECTIVE

To investigate whether magnetic stimulation of the phrenic nerve and multipara esophageal electrode can be used to measure diaphragm compound muscle action potential (CMAP) in intensive care unit (ICU).

METHODS

Ten normal subjects and 10 patients in ICU were studied. A newly designed multipara esophageal catheter with 5 pairs of electrodes was used to record the diaphragm CMAP elicited by magnetic stimulation and transcutaneous electrical stimulation of the phrenic nerve.

RESULTS

Good quality CMAPs were obtained from normal subjects and patients in ICU. In normal subjects, the phrenic nerve conduction time (PNCT) and amplitude of the diaphragm CMAP measured with electrical stimulation [(7.2 +/- 0.8) ms, (1.52 +/- 0.40) mV] were similar to those measured with magnetic stimulation [(7.1 +/- 0.8) ms, (1.56 +/- 0.38) mV, all P > 0.05, pooled left and right values]. The amplitude of the diaphragm CMAP in patients [(0.73 +/- 0.38) mV] was much smaller than that in normal subjects [(1.58 +/- 0.38) mV, P < 0.01, pooled left and right values].

CONCLUSION

This study suggests that magnetic stimulation combined with a multipara esophageal electrode could be a useful technique in assessing diaphragm function in ICU.

Motor control of the costal and crural diaphragm – insights from transcranial magnetic stimulation in man

The costal and crural parts of the diaphragm differ in their embryological development and physiological function. It is not known if this is reflected in differences in their motor cortical representation. We compared the response of the costal and crural diaphragms using varying intensities of transcranial magnetic stimulation of the motor cortex at rest and during submaximal and maximal inspiratory efforts. The costal and crural motor evoked potential recruitment curves during submaximal inspiratory efforts were similar. The response to stimulation before, during and at 10 and 30 min after 44 consecutive maximal inspiratory efforts was also the same. Using paired stimulations to investigate intra-cortical facilitatory and inhibitory circuits we found no difference between the costal and crural response with varying interstimulus intervals, or when conditioning and test stimulus intensity were varied. We conclude that supraspinal control of the costal and crural diaphragm is identical during inspiratory tasks.

Effects of injection volume on the tissue dose, dose rate, and therapeutic potential intraperitoneal 32p

Increasing the injection volume had no significant long-term effect on the distribution or tissue dose of intraperitoneal 32P in New Zealand white rabbits. Further, the range of doses and dose rates observed in the rabbit had little effect in vitro against either a human ovarian cancer line or an established Chinese hamster cell line. Demonstrable kill of human ovarian cancer cells was achieved, however, for initial 32P dose rates of 11 and 22 rad/h (0.11 and 0.22 Gy/h). From these results, it is estimated that administered 32P activities ranging from about 75-150 mCi (2.8-5.6 GBq) would be required for significant tumoricidal effects in ovarian cancer patients.

Allogeneic marrow transplantation after total lymphoid irradiation (TLI): effect of dose/fraction, thymic irradiation, delayed marrow infusion, and presensitization

BALB/c mice infused with 30 x 10(6) C57BL/Ka bone marrow (BM) cells 1 day after treatment with fractionated total lymphoid irradiation (TLI) (17 fractions of 200 rads each) became stable mixed chimeras without clinical graft-vs-host disease (GVHD). Mice given 18 fractions of 100, 50, or 25 rads each followed 1 day later by C57BL/Ka BM did not become chimeric, indicating that a critical cumulative radiation dose is required for this effect. Animals given TLI with lead shielding placed over the thymus also developed stable chimerism without GVHD. Thus susceptibility to tolerance induction and protection from GVHD after TLI and allogeneic BM transplantation is not due to alteration of the thymic microenvironment by fractionated irradiation. A delay of 7 or 21 days between completion of TLI and BM administration resulted in a high incidence of graft rejection. Sensitization to minor histocompatibility antigens of the BM donor strain by blood transfusion either before or during TLI resulted in marrow graft rejection in a high percentage of animals.

The significance of free blood in liquid and solid tumours

Impregnation of the vasculature with ink was used to study microvascular changes induced in rats by liquid (ascites) and solid growth of W256 and Y-P388 tumour cells. Ascites fluid produced by both tumours was heavily blood-stained; the deep red colour of solid tumour deposits was similarly due to the presence of free blood. In both types of tumour growth this free blood was due to diapedesis of erythrocytes through tips of capillary sprouts which grow when neovascularization (angiogenesis) occurs in response to any suitable (non-neoplastic or neoplastic) stimulus. Ascites growth of these tumours induced profuse sprouting from the peritoneal capillaries; this sprouting, together with the "bleeding" it caused, were inhibited by local pre-irradiation of the peritoneal vasculature with X-rays before intraperitoneal inoculation of rats with the tumours. Similar angiogenesis with bleeding did not occur following inoculation with an allogeneic tumour in rats which had been previously immunized against the tumour. LI tumour cells (tumour cells lethally irradiated in vitro to destroy their proliferative integrity, but which remain metabolically active) also induced sprouts to grow in close proximity to the implanted LI cells, but heat-killed tumour cells caused no sprouting. The nature and significance of neovascularization of tumours and their so-called "haemorrhagic" growth are discussed.