เรื่องที่2 Pattern of Contraction of the Respiratory Muscles
Inspiratory Muscles
realised as early as John Snow (1858) that deepening anaesthesia was associated with decreased thoracic excursion and that abdominal excursion was well maintained this is due to progressive failure of the intercostal muscles with preservation of diaphragm
in contrast, there is an increase in the thoracic component during IPPV in the anaesthetised paralysed patient
Bryan & Froese (1977) demonstrated that most of the ventilatory response to hypercapnia was due to the rib cage, rather than the abdominal component of total respiratory excursion
this is the basis of the statement that the reduction in the CO2 response is due to inhibition of intercostal muscle activity this loss of intercostal activity may be detrimental in patients with compromised abdominal excursion, or with hyperinflated lungs and flattened diaphragms the other major change is the loss of the tonic activity of the diaphragm, with the resultant decrease in the FRC
Expiratory and Other Muscles
GA results in phasic activity of the expiratory group which are normally silent during the respiratory cycle
this appears to serve no useful purpose and is unrelated to the decrease in FRC this increases abdominal muscle tone in the absence of paralysis
the genioglossus normally rhythmically contracts with respiration loss of tone to this may result in upper airway obstruction
เรื่องที่3 Healthy Interference
RNA controls genes in a way that was only discov ered recently: a process called RNA interference, or RNAi. Although scientists identified RNAi less than 10 years ago, they now know that organisms have been using this trick for millions of years.
Researchers believe that RNAi arose as a way to reduce the production of a gene’s encoded protein for purposes of finetuning growth or selfdefense. When viruses infect cells, for example, they command their host to produce specialized RNAs that allow the virus to survive and make copies of itself. Researchers believe that RNAi eliminates unwanted viral RNA, and some speculate that it may even play a role in human immunity.
Oddly enough, scientists discovered RNAi from a failed experiment! Researchers investigating genes involved in plant growth noticed something strange: When they tried to turn petunia flowers purple by adding an extra “purple” gene, the flowers bloomed white instead.
This result fascinated researchers, who could not understand how adding genetic material could somehow get rid of an inherited trait. The mystery remained unsolved until, a few years later, two geneticists studying development saw a similar thing happening in lab animals.
To their surprise, Mello and Fire found that their antisense RNA tool wasn’t doing much at all. Rather, they determined, a double stranded contaminant produced during the synthesis of the singlestranded antisense RNA interfered with gene expression. Further experiments revealed that the double stranded RNA gets chopped up inside the cell into much smaller pieces that stick to mRNA and block its action, much like the microRNA pieces.
Today, scientists are taking a cue from nature and using RNAi to explore biology. They have learned, for example, that the process is not limited to worms and plants, but operates in humans too. Medical researchers are currently testing new types of RNAibased drugs for treating condi tions such as macular degeneration, the leading cause of blindness, and various infections, includ ing those caused by HIV and the herpes virus.