The healthcare sector was the only category in positive territory on Friday as investors sought defensive stocks in the face of a wider market sell-off.Meanwhile, results from medical devices maker Smith & Nephew were also encouraging investors in the healthcare space after modestly beating forecasts with its second-quarter report.Adjusted earnings per share rose 13% to 20.4 cents in the second quarter as a result of a rebalancing of the business towards higher growth markets. Consensus estimates were for earnings of 19.4 per share.Revenues increased 3% to $1,147m, ahead of the $1,136m forecast."Whilst the performance was slightly mixed, the underlying picture is certainly improving and we continue to see a long-term growth story evolving," said analyst Nicholas Keher from Investec.The stock was up 2.6% at 1,052.3p by 14:04. However, Keher did downgrade the shares from 'buy' to 'add', saying that they "may struggle to break past £11".Other London-listed healthcare stocks were also performing well in afternoon trade, including Synergy Health, Tristel and Bioquell.Defensive sectors such as healthcare usually perform well in times of market volatility as markets tend to favour companies whose products are likely to be resilient to economic uncertainty.Top performing sectors so far todayHealth Care Equipment & Services 5,845.30 +1.66%Bottom performing sectors so far todayForestry & Paper 10,976.01 -2.30%Fixed Line Telecommunications 4,354.88 -2.19%Mining 17,548.14 -2.17%Chemicals 9,541.35 -2.06%Life Insurance 7,014.78 -1.99%BC